Add M25P20-old

This older (ST-branded) revision of M25P20 chip does not support RDID and
hence was not detected correctly. This patch adds a workaround similar
to M25P40-old.

Corresponding to flashrom svn r1652.

Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/flashchips.c b/flashchips.c
index d4ab1be..1c28cb5 100644
--- a/flashchips.c
+++ b/flashchips.c
@@ -8298,7 +8298,7 @@
 	},
 
 	{
-		.vendor		= "ST",
+		.vendor		= "ST", /* Numonyx */
 		.name		= "M25P20",
 		.bustype	= BUS_SPI,
 		.manufacture_id	= ST_ID,
@@ -8319,10 +8319,39 @@
 				.block_erase = spi_block_erase_c7,
 			}
 		},
-		.printlock	= spi_prettyprint_status_register_default_bp3, /* TODO: check */
+		.printlock	= spi_prettyprint_status_register_default_bp1,
 		.unlock		= spi_disable_blockprotect,
 		.write		= spi_chip_write_256,
-		.read		= spi_chip_read,
+		.read		= spi_chip_read, /* Fast read (0x0B) supported */
+		.voltage	= {2700, 3600},
+	},
+
+	{
+		.vendor		= "ST",
+		.name		= "M25P20-old",
+		.bustype	= BUS_SPI,
+		.manufacture_id	= 0, /* Not used. */
+		.model_id	= ST_M25P20_RES,
+		.total_size	= 256,
+		.page_size	= 256,
+		.feature_bits	= FEATURE_WRSR_WREN,
+		.tested		= TEST_OK_PREW,
+		.probe		= probe_spi_res1,
+		.probe_timing	= TIMING_ZERO,
+		.block_erasers	=
+		{
+			{
+				.eraseblocks = { {64 * 1024, 4} },
+				.block_erase = spi_block_erase_d8,
+			}, {
+				.eraseblocks = { {256 * 1024, 1} },
+				.block_erase = spi_block_erase_c7,
+			}
+		},
+		.printlock	= spi_prettyprint_status_register_default_bp1,
+		.unlock		= spi_disable_blockprotect,
+		.write		= spi_chip_write_256,
+		.read		= spi_chip_read, /* Fast read (0x0B) supported */
 		.voltage	= {2700, 3600},
 	},
 
diff --git a/flashchips.h b/flashchips.h
index 1a0696f..c4c72ba 100644
--- a/flashchips.h
+++ b/flashchips.h
@@ -572,6 +572,7 @@
 #define ST_M25P10A		0x2011
 #define ST_M25P10_RES		0x10	/* Same code as M25P05. */
 #define ST_M25P20		0x2012
+#define ST_M25P20_RES		0x11
 #define ST_M25P40		0x2013
 #define ST_M25P40_RES		0x12
 #define ST_M25P80		0x2014