Re: [PATCH] scsi: ufs: mark HPB support as BROKEN

James Bottomley
2021-10-28T20:33:19Z

On Thu, 2021-10-28 at 13:21 -0700, Bart Van Assche wrote:
[...]
> Hi James,
>
> The help with trying to find a solution is appreciated.
>
> One of the software developers who is familiar with HPB explained to
> me that READ BUFFER and WRITE BUFFER commands may be received in an
> arbitrary order by UFS devices. The UFS HPB spec requires UFS devices
> to be able to stash up to 128 such pairs. I'm concerned that leaving
> out WRITE BUFFER commands only will break the HPB protocol in a
> subtle way.

Based on the publicly available information (the hotstorage paper) I
don't belive it can. The Samsung guys also appear to confirm that the
use of WRITE BUFFER is simply an optimzation for large requests:

https://lore.kernel.org/all/20211025051654epcms2p36b259d237eb2b8b885210148118c5d3f@epcms2p3/

As did the excerpt from the spec you posted. It will cause slowdowns
for reads of > 32kb, because they have to go through the native FTL
lookup now, but there shouldn't be any functional change. Unless
there's anything else in the proprietary spec that contradicts this?

James