Re: [PATCH] libata: increase LBA48 max sectors to 65535

[Jeff Garzik <jgarzik@pobox.com>]

Jens Axboe wrote:
> On Thu, Feb 16 2006, Tejun Heo wrote:
> 
>>Jens Axboe wrote:
>>
>>>On Wed, Feb 15 2006, Tejun Heo wrote:
>>>
>>>
>>>>max_hw_sectors/max_sectors separation patch made into the tree,
>>>>increase max_sectors to its hardware limit.
>>>>
>>>>Signed-off-by: Tejun Heo <htejun@gmail.com>
>>>>
>>>>---
>>>>
>>>>Jeff, first of all, thanks for the pointer.  I have two more
>>>>questions.
>>>>
>>>>* I make ATA_MAX_SECTORS_LBA48 65535 (the 0000h case is supposed to be
>>>>broken, right?); however, the comment says 65534.  Should it be
>>>>65534?
>>>
>>>
>>>Since we never noticed any breakage on !sectors on lba28, I think we can
>>>safely assume that !sectors will work fine for lba48 as well. So why not
>>>just make it full 64k, eg 65536? ->max_hw_sectors is an unsigned int
>>>now, so 64k wont overflow it.
>>>
>>
>>Hello, Jens.
>>
>>libata currently sets max_sectors to 200 (ATA_MAX_SECTORS) on lba28. 
>>Are you talking about IDE driver?  IDE driver seems to set max_sectors 
>>to 256 on probe and make it 2048 while setting up ide disk if lba48.
> 
> 
> Yes I mean the IDE driver. The 200 sector value in libata has always
> struck me as being extremely odd and a very bad choice. It's somewhere
> in between reasonable defaults, which isn't very nice. I'd suggest just
> making it 256 as well, unless Jeff has a reason why it's set to 200.

Its set to 200 for a libata-related reason that I now forget :(

It had nothing to do with controllers or devices, hence the FIXME.

As an aside, I wonder if the PRD limit is unnecessarily low.  I don't 
remember seeing anything that claimed we were limited to 256 s/g entries 
in the old IDE docs?

	Jeff