tree 6cff97d21bb2d3648a3103d55cd22b6a4ce1eb6d
parent 61a8bd27fb5ff27db98e96b462957994e7cca946
author Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net> 1236300025 +0000
committer Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net> 1236300025 +0000

Reduce use of volatile variables

During the conversion of flash chip accesses to helper functions, I spotted
assignments to volatile variables which were neither placed inside the mmapped
ROM area nor were they counters.
Due to the use of accessor functions, volatile usage can be reduced
significantly because the accessor functions take care of actually
performing the reads/writes correctly.

The following semantic patch spotted them (linebreak in python string
for readability reasons, please remove before usage):
@r exists@
expression b;
typedef uint8_t;
volatile uint8_t a;
position p1;
@@
 a@p1 = readb(b);

@script:python@
p1 << r.p1;
a << r.a;
b << r.b;
@@
print "* file: %s line %s has assignment to unnecessarily volatile
variable: %s = readb(%s);" % (p1[0].file, p1[0].line, a, b)

Result was:
HANDLING: sst28sf040.c
* file: sst28sf040.c line 44 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 43 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 42 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 41 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 40 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 39 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 38 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 58 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 57 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 56 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 55 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 54 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 53 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);
* file: sst28sf040.c line 52 has assignment to unnecessarily volatile
variable: tmp = readb(TODO: Binary);

The following semantic patch uses the spatch builtin match printing
functionality by prepending a "*" to the line with the pattern:
@@
expression b;
typedef uint8_t;
volatile uint8_t a;
@@
* a = readb(b);

Result is:
HANDLING: sst28sf040.c
diff =
-       tmp = readb(bios + 0x1823);
-       tmp = readb(bios + 0x1820);
-       tmp = readb(bios + 0x1822);
-       tmp = readb(bios + 0x0418);
-       tmp = readb(bios + 0x041B);
-       tmp = readb(bios + 0x0419);
-       tmp = readb(bios + 0x040A);
 }
 
 static __inline__ void unprotect_28sf040(volatile uint8_t *bios)
@@ -49,13 +42,6 @@ static __inline__ void unprotect_28sf040
        /* ask compiler not to optimize this */
        volatile uint8_t tmp;
 
-       tmp = readb(bios + 0x1823);
-       tmp = readb(bios + 0x1820);
-       tmp = readb(bios + 0x1822);
-       tmp = readb(bios + 0x0418);
-       tmp = readb(bios + 0x041B);
-       tmp = readb(bios + 0x0419);
-       tmp = readb(bios + 0x041A);
 }
 
 static __inline__ int erase_sector_28sf040(volatile uint8_t *bios,

It's arguably a bit easier to read if you get used to the leading "-"
for matching lines.

This patch was enabled by Coccinelle:
http://www.emn.fr/x-info/coccinelle/

Corresponding to flashrom svn r419 and coreboot v2 svn r3973.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Joseph Smith <joe@settoplinux.org>