diff --git a/bitbang_spi.c b/bitbang_spi.c
index 7c183c3..ac50e67 100644
--- a/bitbang_spi.c
+++ b/bitbang_spi.c
@@ -64,7 +64,7 @@
 	return master->get_miso();
 }
 
-static int bitbang_spi_send_command(struct flashctx *flash,
+static int bitbang_spi_send_command(const struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
 				    unsigned char *readarr);
@@ -145,7 +145,7 @@
 	}
 }
 
-static int bitbang_spi_send_command(struct flashctx *flash,
+static int bitbang_spi_send_command(const struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
 				    unsigned char *readarr)
diff --git a/buspirate_spi.c b/buspirate_spi.c
index 826bd84..fdfc0e4 100644
--- a/buspirate_spi.c
+++ b/buspirate_spi.c
@@ -128,9 +128,9 @@
 	return ret;
 }
 
-static int buspirate_spi_send_command_v1(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int buspirate_spi_send_command_v1(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 					 const unsigned char *writearr, unsigned char *readarr);
-static int buspirate_spi_send_command_v2(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int buspirate_spi_send_command_v2(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 					 const unsigned char *writearr, unsigned char *readarr);
 
 static struct spi_master spi_master_buspirate = {
@@ -572,7 +572,7 @@
 	return 0;
 }
 
-static int buspirate_spi_send_command_v1(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int buspirate_spi_send_command_v1(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 					 const unsigned char *writearr, unsigned char *readarr)
 {
 	unsigned int i = 0;
@@ -625,7 +625,7 @@
 	return ret;
 }
 
-static int buspirate_spi_send_command_v2(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int buspirate_spi_send_command_v2(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 					 const unsigned char *writearr, unsigned char *readarr)
 {
 	int i = 0, ret = 0;
diff --git a/ch341a_spi.c b/ch341a_spi.c
index d3af32f..17c37eb 100644
--- a/ch341a_spi.c
+++ b/ch341a_spi.c
@@ -335,7 +335,7 @@
 	stored_delay_us += usecs;
 }
 
-static int ch341a_spi_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt, const unsigned char *writearr, unsigned char *readarr)
+static int ch341a_spi_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt, const unsigned char *writearr, unsigned char *readarr)
 {
 	if (handle == NULL)
 		return -1;
diff --git a/chipdrivers.h b/chipdrivers.h
index cb1e877..3c7d146 100644
--- a/chipdrivers.h
+++ b/chipdrivers.h
@@ -62,8 +62,8 @@
 
 
 /* spi25_statusreg.c */
-uint8_t spi_read_status_register(struct flashctx *flash);
-int spi_write_status_register(struct flashctx *flash, int status);
+uint8_t spi_read_status_register(const struct flashctx *flash);
+int spi_write_status_register(const struct flashctx *flash, int status);
 void spi_prettyprint_status_register_bit(uint8_t status, int bit);
 int spi_prettyprint_status_register_plain(struct flashctx *flash);
 int spi_prettyprint_status_register_default_welwip(struct flashctx *flash);
diff --git a/dediprog.c b/dediprog.c
index 99df7b0..bacb6b8 100644
--- a/dediprog.c
+++ b/dediprog.c
@@ -714,7 +714,7 @@
 	return dediprog_spi_write(flash, buf, start, len, WRITE_MODE_2B_AAI);
 }
 
-static int dediprog_spi_send_command(struct flashctx *flash,
+static int dediprog_spi_send_command(const struct flashctx *flash,
 				     unsigned int writecnt,
 				     unsigned int readcnt,
 				     const unsigned char *writearr,
diff --git a/digilent_spi.c b/digilent_spi.c
index 13a876e..0f7a9da 100644
--- a/digilent_spi.c
+++ b/digilent_spi.c
@@ -257,7 +257,7 @@
 	return 0;
 }
 
-static int digilent_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int digilent_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				     const unsigned char *writearr, unsigned char *readarr)
 {
 	int ret;
diff --git a/dummyflasher.c b/dummyflasher.c
index b9f6126..e1a1d80 100644
--- a/dummyflasher.c
+++ b/dummyflasher.c
@@ -93,7 +93,7 @@
 
 static unsigned int spi_write_256_chunksize = 256;
 
-static int dummy_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int dummy_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				  const unsigned char *writearr, unsigned char *readarr);
 static int dummy_spi_write_256(struct flashctx *flash, const uint8_t *buf,
 			       unsigned int start, unsigned int len);
@@ -818,7 +818,7 @@
 }
 #endif
 
-static int dummy_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int dummy_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *writearr,
 				  unsigned char *readarr)
diff --git a/flash.h b/flash.h
index 1a9bd9f..2f0143b 100644
--- a/flash.h
+++ b/flash.h
@@ -415,8 +415,8 @@
 	unsigned char *readarr;
 };
 #define NULL_SPI_CMD { 0, 0, NULL, NULL, }
-int spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt, const unsigned char *writearr, unsigned char *readarr);
-int spi_send_multicommand(struct flashctx *flash, struct spi_command *cmds);
+int spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt, const unsigned char *writearr, unsigned char *readarr);
+int spi_send_multicommand(const struct flashctx *flash, struct spi_command *cmds);
 
 enum chipbustype get_buses_supported(void);
 #endif				/* !__FLASH_H__ */
diff --git a/ft2232_spi.c b/ft2232_spi.c
index 5bdc2a7..d63aa8d 100644
--- a/ft2232_spi.c
+++ b/ft2232_spi.c
@@ -148,7 +148,7 @@
 	return 0;
 }
 
-static int ft2232_spi_send_command(struct flashctx *flash,
+static int ft2232_spi_send_command(const struct flashctx *flash,
 				   unsigned int writecnt, unsigned int readcnt,
 				   const unsigned char *writearr,
 				   unsigned char *readarr);
@@ -447,7 +447,7 @@
 }
 
 /* Returns 0 upon success, a negative number upon errors. */
-static int ft2232_spi_send_command(struct flashctx *flash,
+static int ft2232_spi_send_command(const struct flashctx *flash,
 				   unsigned int writecnt, unsigned int readcnt,
 				   const unsigned char *writearr,
 				   unsigned char *readarr)
diff --git a/ichspi.c b/ichspi.c
index 725bfb3..15222d8 100644
--- a/ichspi.c
+++ b/ichspi.c
@@ -1103,7 +1103,7 @@
 	}
 }
 
-static int ich_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int ich_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				unsigned int readcnt,
 				const unsigned char *writearr,
 				unsigned char *readarr)
@@ -1507,7 +1507,7 @@
 	return 0;
 }
 
-static int ich_spi_send_multicommand(struct flashctx *flash,
+static int ich_spi_send_multicommand(const struct flashctx *flash,
 				     struct spi_command *cmds)
 {
 	int ret = 0;
diff --git a/it85spi.c b/it85spi.c
index 5ce9193..b998790 100644
--- a/it85spi.c
+++ b/it85spi.c
@@ -270,7 +270,7 @@
 	return 0;
 }
 
-static int it85xx_spi_send_command(struct flashctx *flash,
+static int it85xx_spi_send_command(const struct flashctx *flash,
 				   unsigned int writecnt, unsigned int readcnt,
 				   const unsigned char *writearr,
 				   unsigned char *readarr);
@@ -322,7 +322,7 @@
  *   3. read date from LPC/FWH address 0xffff_fdxxh (drive CE# low and get
  *      data from MISO)
  */
-static int it85xx_spi_send_command(struct flashctx *flash,
+static int it85xx_spi_send_command(const struct flashctx *flash,
 				   unsigned int writecnt, unsigned int readcnt,
 				   const unsigned char *writearr,
 				   unsigned char *readarr)
diff --git a/it87spi.c b/it87spi.c
index 7b38492..c1ed29c 100644
--- a/it87spi.c
+++ b/it87spi.c
@@ -98,7 +98,7 @@
 	return;
 }
 
-static int it8716f_spi_send_command(struct flashctx *flash,
+static int it8716f_spi_send_command(const struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
 				    unsigned char *readarr);
@@ -276,7 +276,7 @@
  * commands with the address in inverse wire order. That's why the register
  * ordering in case 4 and 5 may seem strange.
  */
-static int it8716f_spi_send_command(struct flashctx *flash,
+static int it8716f_spi_send_command(const struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
 				    unsigned char *readarr)
diff --git a/jlink_spi.c b/jlink_spi.c
index 00e9c6d..3a73c01 100644
--- a/jlink_spi.c
+++ b/jlink_spi.c
@@ -101,7 +101,7 @@
 	return true;
 }
 
-static int jlink_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int jlink_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 		const unsigned char *writearr, unsigned char *readarr)
 {
 	uint32_t length;
diff --git a/linux_spi.c b/linux_spi.c
index aa73c18..1ef8f2b 100644
--- a/linux_spi.c
+++ b/linux_spi.c
@@ -49,7 +49,7 @@
 static size_t max_kernel_buf_size;
 
 static int linux_spi_shutdown(void *data);
-static int linux_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int linux_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *txbuf,
 				  unsigned char *rxbuf);
@@ -183,7 +183,7 @@
 	return 0;
 }
 
-static int linux_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int linux_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *txbuf,
 				  unsigned char *rxbuf)
diff --git a/mstarddc_spi.c b/mstarddc_spi.c
index db11157..48d6204 100644
--- a/mstarddc_spi.c
+++ b/mstarddc_spi.c
@@ -153,7 +153,7 @@
 }
 
 /* Returns 0 upon success, a negative number upon errors. */
-static int mstarddc_spi_send_command(struct flashctx *flash,
+static int mstarddc_spi_send_command(const struct flashctx *flash,
 				     unsigned int writecnt,
 				     unsigned int readcnt,
 				     const unsigned char *writearr,
diff --git a/pickit2_spi.c b/pickit2_spi.c
index 2936ee8..0bc17af 100644
--- a/pickit2_spi.c
+++ b/pickit2_spi.c
@@ -195,7 +195,7 @@
 	return 0;
 }
 
-static int pickit2_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int pickit2_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				     const unsigned char *writearr, unsigned char *readarr)
 {
 
diff --git a/programmer.h b/programmer.h
index 3cf53b9..f1915df 100644
--- a/programmer.h
+++ b/programmer.h
@@ -600,9 +600,9 @@
 	uint32_t features;
 	unsigned int max_data_read; // (Ideally,) maximum data read size in one go (excluding opcode+address).
 	unsigned int max_data_write; // (Ideally,) maximum data write size in one go (excluding opcode+address).
-	int (*command)(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+	int (*command)(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 		   const unsigned char *writearr, unsigned char *readarr);
-	int (*multicommand)(struct flashctx *flash, struct spi_command *cmds);
+	int (*multicommand)(const struct flashctx *flash, struct spi_command *cmds);
 
 	/* Optimized functions for this master */
 	int (*read)(struct flashctx *flash, uint8_t *buf, unsigned int start, unsigned int len);
@@ -611,9 +611,9 @@
 	const void *data;
 };
 
-int default_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+int default_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 			     const unsigned char *writearr, unsigned char *readarr);
-int default_spi_send_multicommand(struct flashctx *flash, struct spi_command *cmds);
+int default_spi_send_multicommand(const struct flashctx *flash, struct spi_command *cmds);
 int default_spi_read(struct flashctx *flash, uint8_t *buf, unsigned int start, unsigned int len);
 int default_spi_write_256(struct flashctx *flash, const uint8_t *buf, unsigned int start, unsigned int len);
 int default_spi_write_aai(struct flashctx *flash, const uint8_t *buf, unsigned int start, unsigned int len);
diff --git a/sb600spi.c b/sb600spi.c
index cb5c4a4..21f22f6 100644
--- a/sb600spi.c
+++ b/sb600spi.c
@@ -56,9 +56,9 @@
 #define FIFO_SIZE_OLD		8
 #define FIFO_SIZE_YANGTZE	71
 
-static int sb600_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int sb600_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				  const unsigned char *writearr, unsigned char *readarr);
-static int spi100_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int spi100_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				  const unsigned char *writearr, unsigned char *readarr);
 
 static struct spi_master spi_master_sb600 = {
@@ -190,7 +190,7 @@
 }
 
 /* Check the number of bytes to be transmitted and extract opcode. */
-static int check_readwritecnt(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt)
+static int check_readwritecnt(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt)
 {
 	unsigned int maxwritecnt = flash->mst->spi.max_data_write + 3;
 	if (writecnt > maxwritecnt) {
@@ -217,7 +217,7 @@
 	msg_pspew("done\n");
 }
 
-static int sb600_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int sb600_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *writearr,
 				  unsigned char *readarr)
@@ -303,7 +303,7 @@
 	return 0;
 }
 
-static int spi100_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int spi100_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *writearr,
 				  unsigned char *readarr)
diff --git a/serprog.c b/serprog.c
index 37a9db4..1befce1 100644
--- a/serprog.c
+++ b/serprog.c
@@ -295,7 +295,7 @@
 	return 0;
 }
 
-static int serprog_spi_send_command(struct flashctx *flash,
+static int serprog_spi_send_command(const struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
 				    unsigned char *readarr);
@@ -894,7 +894,7 @@
 	sp_prev_was_write = 0;
 }
 
-static int serprog_spi_send_command(struct flashctx *flash,
+static int serprog_spi_send_command(const struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
 				    unsigned char *readarr)
diff --git a/spi.c b/spi.c
index 489baf3..aed2a92 100644
--- a/spi.c
+++ b/spi.c
@@ -26,7 +26,7 @@
 #include "programmer.h"
 #include "spi.h"
 
-int spi_send_command(struct flashctx *flash, unsigned int writecnt,
+int spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 		     unsigned int readcnt, const unsigned char *writearr,
 		     unsigned char *readarr)
 {
@@ -34,12 +34,12 @@
 				       readarr);
 }
 
-int spi_send_multicommand(struct flashctx *flash, struct spi_command *cmds)
+int spi_send_multicommand(const struct flashctx *flash, struct spi_command *cmds)
 {
 	return flash->mst->spi.multicommand(flash, cmds);
 }
 
-int default_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+int default_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 			     unsigned int readcnt,
 			     const unsigned char *writearr,
 			     unsigned char *readarr)
@@ -60,7 +60,7 @@
 	return spi_send_multicommand(flash, cmd);
 }
 
-int default_spi_send_multicommand(struct flashctx *flash,
+int default_spi_send_multicommand(const struct flashctx *flash,
 				  struct spi_command *cmds)
 {
 	int result = 0;
diff --git a/spi25_statusreg.c b/spi25_statusreg.c
index bb09e58..34f9ad4 100644
--- a/spi25_statusreg.c
+++ b/spi25_statusreg.c
@@ -22,7 +22,7 @@
 #include "spi.h"
 
 /* === Generic functions === */
-static int spi_write_status_register_flag(struct flashctx *flash, int status, const unsigned char enable_opcode)
+static int spi_write_status_register_flag(const struct flashctx *flash, int status, const unsigned char enable_opcode)
 {
 	int result;
 	int i = 0;
@@ -73,7 +73,7 @@
 	return 0;
 }
 
-int spi_write_status_register(struct flashctx *flash, int status)
+int spi_write_status_register(const struct flashctx *flash, int status)
 {
 	int feature_bits = flash->chip->feature_bits;
 	int ret = 1;
@@ -90,7 +90,7 @@
 	return ret;
 }
 
-uint8_t spi_read_status_register(struct flashctx *flash)
+uint8_t spi_read_status_register(const struct flashctx *flash)
 {
 	static const unsigned char cmd[JEDEC_RDSR_OUTSIZE] = { JEDEC_RDSR };
 	/* FIXME: No workarounds for driver/hardware bugs in generic code. */
diff --git a/stlinkv3_spi.c b/stlinkv3_spi.c
index d2988b6..d56f305 100644
--- a/stlinkv3_spi.c
+++ b/stlinkv3_spi.c
@@ -323,7 +323,7 @@
 	return 0;
 }
 
-static int stlinkv3_spi_transmit(struct flashctx *flash,
+static int stlinkv3_spi_transmit(const struct flashctx *flash,
 				 unsigned int write_cnt,
 				 unsigned int read_cnt,
 				 const unsigned char *write_arr,
diff --git a/usbblaster_spi.c b/usbblaster_spi.c
index e2a0a4f..46de86c 100644
--- a/usbblaster_spi.c
+++ b/usbblaster_spi.c
@@ -179,7 +179,7 @@
 }
 
 /* Returns 0 upon success, a negative number upon errors. */
-static int usbblaster_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int usbblaster_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				       const unsigned char *writearr, unsigned char *readarr)
 {
 	uint8_t cmd;
diff --git a/wbsio_spi.c b/wbsio_spi.c
index f4f6af9..1674825 100644
--- a/wbsio_spi.c
+++ b/wbsio_spi.c
@@ -57,7 +57,7 @@
 	return flashport;
 }
 
-static int wbsio_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int wbsio_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *writearr,
 				  unsigned char *readarr);
@@ -110,7 +110,7 @@
  * Would one more byte of RAM in the chip (to get all 24 bits) really make
  * such a big difference?
  */
-static int wbsio_spi_send_command(struct flashctx *flash, unsigned int writecnt,
+static int wbsio_spi_send_command(const struct flashctx *flash, unsigned int writecnt,
 				  unsigned int readcnt,
 				  const unsigned char *writearr,
 				  unsigned char *readarr)