Re: [PATCH] libata: add support for READ/WRITE LONG

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Mark Lord wrote:
> Alan Cox wrote:
> 
>>> The fussy bit is that these commands require a non-standard
>>> sector size, usually 520 bytes instead of 512.

>> Do we always know the worst case here as this breaks my pending patch to
>> use bounce buffers for PIO so we transfer with IRQ enabled and I need to
>> know the correct new worst case size.

> Ugh.  The drives default to 520 bytes (always),

    The old IDE drives used to have 4 and 7 byte ECC (seen in ancient Phoenix 
BIOS).

> but can specify a different, preferred, length in
> the IDENTIFY data.  A SETFEATURES command is required
> to change the setting from the default of 520.

    You're wrong here (which is explainable by your patch bneing boken 
protocol wise) -- there used to be two subcodes, one to selecyt vendor spcific 
length (0x44), and one to selectt 4-byte ECC (0xBB). Not 8-byte!

> In practice, I only ever use 520, because (1) it always works,
> and (2) I'm only trying to corrupt drives, not write correct stuff. ;)

> So we could modify the patch to limit it to a specific maximum,
> or always require exactly 520 bytes without any hardship.

> ???

    Certainly not the second. Vendor ECC length is indicated in the word 22 
identify device info. Not sure how this gets translated to SCSI...

WBR, Sergei