Re: [PATCH 05/13] libata: improve ATAPI draining

[Tejun Heo <htejun@gmail.com>]

Tejun Heo wrote:
> Albert Lee wrote:
>> If the trailing data is odd-lengthed, normally the situation is that
>> we have odd-lengthed real data before the trailing data. e.g. The real
>> data is 9 bytes, but the drive returns 10 bytes (so, the trailing data
>> is 1 byte).
>>
>> In ata_data_xfer(), we have the following code:
>>
>>     /* Transfer trailing 1 byte, if any. */
>>     ... (for write case) ...
>>     iowrite16(le16_to_cpu(align_buf[0]), ap->ioaddr.data_addr);  or
>>
>>     ... (for read case) ...
>>     ioread16(ap->ioaddr.data_addr)
>>
>> The PATA bus is actually 16-bit wide. So, ata_data_xfer() actually
>> implicitly transfers one more byte than we see if it's odd-lengthed.
>>
>> That's why in atapi_pio_bytes(), the trailing length was round down
>> instead round up.
> 
> Hmmm... it's tricky.  When draining a partial chunk because of
> odd-length short buffer on even-length chunk, it needs to be rounded
> down but on all other cases it needs to be rounded up, right?
> 
> This is basically because count isn't updated with actually consumed
> number of bytes.  I'll fix it and post an updated patch.

Okay, updated patchset posted.  Albert, can you please review the new one?

Thanks.

-- 
tejun