linux-kernel - RE: [PATCH] mmc: block: disable the reliable write If the card does not support CMD23

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Date:	Fri, 28 Aug 2015 08:38:22 +0800
From:	LIYONG <sdliyong@...il.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
CC:	Chris Ball <chris@...ntf.net>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] mmc: block: disable the reliable write If the card does
 not support CMD23

Hi Uffe,

Since Reliable Write depends on the CMD23. I think we need to disable Reliable Write if the card does not support CMD23(due to performance impact issue), so I add this patch.

Do you think we still need to enable Reliable Write even if the card does not support CMD23?

Thanks,
Yong Li
----------------------------------------
> Date: Thu, 27 Aug 2015 15:22:44 +0200
> Subject: Re: [PATCH] mmc: block: disable the reliable write If the card does not support CMD23
> From: ulf.hansson@...aro.org
> To: sdliyong@...il.com
> CC: chris@...ntf.net; linux-mmc@...r.kernel.org; linux-kernel@...r.kernel.org
>
> On 25 August 2015 at 14:06, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 14 August 2015 at 09:30, <sdliyong@...il.com> wrote:
>>> From: Yong Li <sdliyong@...il.com>
>>>
>>> Signed-off-by: Yong Li <sdliyong@...il.com>
>>> ---
>>> drivers/mmc/card/block.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>>> index 452782b..d9e3c45 100644
>>> --- a/drivers/mmc/card/block.c
>>> +++ b/drivers/mmc/card/block.c
>>> @@ -1366,7 +1366,8 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
>>> bool do_rel_wr = ((req->cmd_flags & REQ_FUA) ||
>>> (req->cmd_flags & REQ_META)) &&
>>> (rq_data_dir(req) == WRITE) &&
>>> - (md->flags & MMC_BLK_REL_WR);
>>> + (md->flags & MMC_BLK_REL_WR) &&
>>> + !(card->quirks & MMC_QUIRK_BLK_NO_CMD23);
>>
>> Further down in mmc_blk_rw_rq_prep() we check for
>> MMC_QUIRK_BLK_NO_CMD23. That check becomes redundant after this
>> change, please remove that check as a part of this patch as well.
>>
>>>
>>> memset(brq, 0, sizeof(struct mmc_blk_request));
>>> brq->mrq.cmd = &brq->cmd;
>>> --
>>> 2.1.0
>>>
>>
>
> Please ignore my previous answer. MMC_QUIRK_BLK_NO_CMD23 is intended
> to indicate to the mmc block layer whether using CMD23 for regular
> block IO request could have a performance impact for some cards. If
> that's the case we don't use it - except when using reliable write!
>
> So this patch is just plain wrong.
>
> Kind regards
> Uffe
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