Re: [PATCH 3/4] libata: Report zeroed read after Trim and max discard size

[Mark Lord <kernel@teksavvy.com>]

Christoph Hellwig wrote:
> On Sat, Nov 21, 2009 at 03:16:05PM -0500, Martin K. Petersen wrote:
>> I was trying to help Eric figure out why his drive pooped on big Trim
>> requests.  For WRITE SAME the limit is inherent in the arguments,
>> whereas our SATL implementation is limited by the 512-byte WRITE SAME
>> payload.  So I needed a way to convey this up the stack.
>>
>> Since you already return a B0 VPD page I thought it would be a
>> convenient place to communicate the max without having to tweak the
>> queue limits directly from within libata.
>>
>> You are right that I'm relying on fuzziness in SBC which requires both
>> the max LBA count and the descriptor count to be specified for UNMAP.
> 
> I think the better way is to make sure we can support any TRIM that
> can be sent down.  Given that TRIM is not NCQ-capable we can just
> allocate one buffer for the TRIM ranges per TRIM capable device.
..

Good approach.

I suppose that buffer would be only 512 bytes long, per device?
That might be a bit restrictive, as TRIM can handle much larger
requests, and some drives (Indinlinx-based at least) prefer large
TRIM lists at present.

On the other hand, the Marvell chipsets cannot handle more than a
single sector of data without first fixing the driver to work around
chipset bugs.  That's probably unique to sata_mv, though.

Cheers

Mark Lord