Issue in oamp nand driver with 32-bit reads in prefetch mode

[Steve Sakoman]

On Wed, Dec 23, 2009 at 9:44 AM, Tony Lindgren <tony at atomide.com> wrote:
> * Vimal Singh <vimal.newwork at gmail.com> [091223 01:32]:
>> In omap nand driver we used to do 32-bit reads (in function
>> omap_read_buf_pref, using 'ioread32_rep' i.e.: __raw_readsl), and it
>> was working fine till some time back. But now, somehow, this has got
>> some problem. Reads are not being done successfully, and driver gives
>> lots for error reprot like below:
>>
>> td->read(0x604 bytes from 0x1fc) returned ECC error
>> uncorrectable error :
>> uncorrectable error :
>> uncorrectable error :
>> uncorrectable error :
>> uncorrectable error :
>> uncorrectable error :
>> mtd->read(0x520 bytes from 0x2e0) returned ECC error
>>
>> While if we change 32-bit reads to 16-bit reads (using 'ioread16_rep'
>> i.e.: __raw_readwl) makes it working fine. (A patch to do this is
>> listed below at the bottom of this mail.)
>>
>> I have not seen any change in routine '__raw_readsl'.
>> So, could someone help me find out the root cause the issue?
>>
>> Thanks for any input.
>
> Maybe an issue with the GPMC timings?

I can confirm that this issue exists on Overo too.  Sadly, switching
to 16 bit reads does not fix the issue for me.  I'll start digging to
see if I can find what's broken.

Steve


> Regards,
>
> Tony
>
>>
>> --
>> Regards,
>> Vimal Singh
>>
>> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
>> index aaef170..dc493f5 100644
>> --- a/drivers/mtd/nand/omap2.c
>> +++ b/drivers/mtd/nand/omap2.c
>> @@ -288,14 +288,14 @@ static void omap_read_buf_pref(struct mtd_info
>>                                               struct omap_nand_info, mtd);
>>       uint32_t pfpw_status = 0, r_count = 0;
>>       int ret = 0;
>> -     u32 *p = (u32 *)buf;
>> +     u16 *p = (u16 *)buf;
>>
>>       /* take care of subpage reads */
>> -     for (; len % 4 != 0; ) {
>> +     for (; len % 2 != 0; ) {
>>               *buf++ = __raw_readb(info->nand.IO_ADDR_R);
>>               len--;
>>       }
>> -     p = (u32 *) buf;
>> +     p = (u16 *) buf;
>>
>>       /* configure and start prefetch transfer */
>>       ret = gpmc_prefetch_enable(info->gpmc_cs, 0x0, len, 0x0);
>> @@ -308,10 +308,10 @@ static void omap_read_buf_pref(struct mtd_info
>> *mtd, u_char *buf, int len)
>>       } else {
>>               do {
>>                       pfpw_status = gpmc_prefetch_status();
>> -                     r_count = ((pfpw_status >> 24) & 0x7F) >> 2;
>> -                     ioread32_rep(info->nand_pref_fifo_add, p, r_count);
>> +                     r_count = ((pfpw_status >> 24) & 0x7F) >> 1;
>> +                     ioread16_rep(info->nand_pref_fifo_add, p, r_count);
>>                       p += r_count;
>> -                     len -= r_count << 2;
>> +                     len -= r_count << 1;
>>               } while (len);
>>
>>               /* disable and stop the PFPW engine */
>> --
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