[U-Boot-Users] [PATCH] Fixed cfi flash read uchar bug.

[Zhang Wei-r63237 <Wei.Zhang@freescale.com>]

Hi, Wolfgang,

Any feedback about this mail?

Thanks!

Zhang Wei 

> -----Original Message-----
> From: u-boot-users-bounces at lists.sourceforge.net 
> [mailto:u-boot-users-bounces at lists.sourceforge.net] On Behalf 
> Of Zhang Wei
> Sent: Tuesday, December 26, 2006 2:05 PM
> To: Wolfgang Denk
> Cc: u-boot-users at lists.sourceforge.net
> Subject: Re: [U-Boot-Users] [PATCH] Fixed cfi flash read uchar bug.
> 
> Hi, Wolfgang,
> 
> Wolfgang Denk wrote:
> > Now this is what I want to understand. What exactly is the 
> "potential
> > problem"?
> >   
> That's the issue in the flash 'Spinsion S29GL064M90TFIR6' with x16 
> connection. After running flash_read_jedec_ids(), any follow 
> CFI query 
> command will get the data with high 8bit = 0xff, but the low 8bit is 
> valid. And if we only read low 8bit, we'll get the 0xff too. In 
> addition, the second follow CFI query command has no that 
> issue. So, I 
> read the full 16bit date and only take the valid low 8bit.
> > Can you please point out which specific part of the Linux 
> MTD code you
> > mean? And which version of the code?
> >   
> The reference codes is in Linux Kernel 2.6.19.
> 
> drivers/mtd/chips/cfi_probe.c: cfi_chip_setup() calls:
>     int num_erase_regions = cfi_read_query(map, base + (0x10 + 
> 28)*ofs_factor);
> include/linux/mtd/cfi.h: cfi_read_query() calls:
>     map_word val = map_read(map, addr);
> include/linux/mtd/map.h defines:
>     #define map_read(map, ofs) inline_map_read(map, ofs)
> include/linux/mtd/map.h: function inline_map_read() body:
> static inline map_word inline_map_read(struct map_info *map, unsigned 
> long ofs)
> {
>     map_word r;
> 
>     if (map_bankwidth_is_1(map))
>         r.x[0] = __raw_readb(map->virt + ofs);
>     else if (map_bankwidth_is_2(map))
>         r.x[0] = __raw_readw(map->virt + ofs);
>     else if (map_bankwidth_is_4(map))
>         r.x[0] = __raw_readl(map->virt + ofs);
> #if BITS_PER_LONG >= 64
>     else if (map_bankwidth_is_8(map))
>         r.x[0] = __raw_readq(map->virt + ofs);
> #endif
>     else if (map_bankwidth_is_large(map))
>         memcpy_fromio(r.x, map->virt+ofs, map->bankwidth);
> 
>     return r;
> }
> And the 'map_word' definition in include/linux/mtd/map.h is below:
> typedef union {
>     unsigned long x[MAX_MAP_LONGS];
> } map_word;
> 
> > I have to admit that I don't really understand this. I would not be
> > surprised that some statement like this can be found in some chip
> > errata, but I would like to know this for certain first.
> >   
> I only find one clue from 'Spinsion S29GL064M90TFIR6' specification, 
> which is the comment 'Data bits DQ15?DQ8 are don?t care. ' 
> for 'RESET' 
> command. And the comment has not found in some other AMD, 
> Spinsion chips 
> specifications.
> > For me this is an indication that the problem is  actually  
> somewhere
> > else,  and while your modification might actually fix the 
> symptoms, I
> > doubt that it is the correct fix - or the correct  problem. 
>  If  your
> > explanation was right, this should not depend on compiler versions.
> >   
> 
> This is a real weird issue. The compiler is also a factor. Chris's 
> different compilers get the different results. In fact, the same gcc 
> with different size codes will also get different results.
> 
> Thanks!
> 
> Best Regards,
> Zhang Wei
> 
> 
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