Re: [Qemu-devel] [PATCH v5 11/24] hw/nand.c: bug fix to BUSY/READY status bit

[Kuo-Jung Su]

2013/3/1 Peter Maydell <address@hidden>:
> On 27 February 2013 07:15, Kuo-Jung Su <address@hidden> wrote:
>> From: Kuo-Jung Su <address@hidden>
>
> Your subject line could be made a little more specific, like this:
> "hw/nand.c: correct the sense of the BUSY/READY status bit".
>

Got it, thanks

>> The BIT6 of Status Register(SR):
>>
>> SR[6] behaves the same as R/B# pin
>>     SR[6] = 0 indicates the device is busy;
>>     SR[6] = 1 means the device is ready
>>
>> Some NAND flash controller (i.e. ftnandc021) relies on the SR[6]
>> to determine if the NAND flash erase/program is success or error timeout.
>>
>> P.S:
>> The exmaple NAND flash datasheet could be found at following link:
>> http://www.mxic.com.tw/QuickPlace/hq/PageLibrary4825740B00298A3B.nsf/h_Index/8FEA549237D2F7674825795800104C26/$File/MX30LF1G08AA,%203V,%201Gb,%20v1.1.pdf
>>
>> Signed-off-by: Kuo-Jung Su <address@hidden>
>> ---
>>  hw/nand.c |   20 +++++++++++++++++---
>>  1 file changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/nand.c b/hw/nand.c
>> index 4a71265..7f40ebf 100644
>> --- a/hw/nand.c
>> +++ b/hw/nand.c
>> @@ -46,7 +46,7 @@
>>  # define NAND_IOSTATUS_PLANE1  (1 << 2)
>>  # define NAND_IOSTATUS_PLANE2  (1 << 3)
>>  # define NAND_IOSTATUS_PLANE3  (1 << 4)
>> -# define NAND_IOSTATUS_BUSY    (1 << 6)
>> +# define NAND_IOSTATUS_READY    (1 << 6)
>>  # define NAND_IOSTATUS_UNPROTCT        (1 << 7)
>>
>>  # define MAX_PAGE              0x800
>> @@ -231,6 +231,7 @@ static void nand_reset(DeviceState *dev)
>>      s->iolen = 0;
>>      s->offset = 0;
>>      s->status &= NAND_IOSTATUS_UNPROTCT;
>> +    s->status |= NAND_IOSTATUS_READY;
>>  }
>
> These two parts look good.
>
>>
>>  static inline void nand_pushio_byte(NANDFlashState *s, uint8_t value)
>> @@ -647,6 +648,8 @@ static void glue(nand_blk_write_, 
>> PAGE_SIZE)(NANDFlashState *s)
>>      if (PAGE(s->addr) >= s->pages)
>>          return;
>>
>> +    s->status &= ~NAND_IOSTATUS_READY;
>> +
>>      if (!s->bdrv) {
>>          mem_and(s->storage + PAGE_START(s->addr) + (s->addr & PAGE_MASK) +
>>                          s->offset, s->io, s->iolen);
>> @@ -656,7 +659,7 @@ static void glue(nand_blk_write_, 
>> PAGE_SIZE)(NANDFlashState *s)
>>          soff = SECTOR_OFFSET(s->addr);
>>          if (bdrv_read(s->bdrv, sector, iobuf, PAGE_SECTORS) < 0) {
>>              printf("%s: read error in sector %" PRIu64 "\n", __func__, 
>> sector);
>> -            return;
>> +            goto blkw_out;
>>          }
>>
>>          mem_and(iobuf + (soff | off), s->io, MIN(s->iolen, PAGE_SIZE - 
>> off));
>> @@ -675,7 +678,7 @@ static void glue(nand_blk_write_, 
>> PAGE_SIZE)(NANDFlashState *s)
>>          soff = off & 0x1ff;
>>          if (bdrv_read(s->bdrv, sector, iobuf, PAGE_SECTORS + 2) < 0) {
>>              printf("%s: read error in sector %" PRIu64 "\n", __func__, 
>> sector);
>> -            return;
>> +            goto blkw_out;
>>          }
>>
>>          mem_and(iobuf + soff, s->io, s->iolen);
>> @@ -685,6 +688,9 @@ static void glue(nand_blk_write_, 
>> PAGE_SIZE)(NANDFlashState *s)
>>          }
>>      }
>>      s->offset = 0;
>> +
>> +blkw_out:
>> +    s->status |= NAND_IOSTATUS_READY;
>>  }
>
> How is it ever possible for a guest to observe the status register
> in the state where the READY bit is cleared? There's no point in
> clearing the bit on entry to this function and setting it again
> on every exit path when nobody will ever read the status register
> while we're inside the function. (Same comments apply for read
> and erase.)
>

Got it, thanks.
I'll remove the code for clear/set SR[6] from the read/erase/write functions.

> thanks
> -- PMM



-- 
Best wishes,
Kuo-Jung Su