linux-kernel - RE: [PATCH v6 2/3] mmc: core: Support packed write command for eMMC4.5 device

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Message-ID: <1acdc97ed00d55604beb322555a37d75.squirrel@www.codeaurora.org>
Date:	Tue, 5 Jun 2012 13:05:07 -0700 (PDT)
From:	merez@...eaurora.org
To:	"Seungwon Jeon" <tgih.jun@...sung.com>
Cc:	merez@...eaurora.org, linux-mmc@...r.kernel.org,
	"'Chris Ball'" <cjb@...top.org>, linux-kernel@...r.kernel.org
Subject: RE: [PATCH v6 2/3] mmc: core: Support packed write command for 
     eMMC4.5 device


> Maya Erez <merez@...eaurora.org> wrote:
>> > Maya Erez <merez@...eaurora.org> wrote:
>> >> > @@ -1313,10 +1609,17 @@ static int mmc_blk_issue_rw_rq(struct
>> >> mmc_queue
>> >> *mq, struct request *rqc)
>> >> >  			 * A block was successfully transferred.
>> >> >  			 */
>> >> >  			mmc_blk_reset_success(md, type);
>> >> > -			spin_lock_irq(&md->lock);
>> >> > -			ret = __blk_end_request(req, 0,
>> >> > +
>> >> > +			if (mq_rq->packed_cmd != MMC_PACKED_NONE) {
>> >> > +				ret = mmc_blk_end_packed_req(mq, mq_rq);
>> >> If a specific request in the packed request consistantly fails, there
>> is
>> >> nothing to stop us from sending the same packed request in an endless
>> >> loop.
>> > There is various error case. This patch reused the existing error
>> > handling.
>> > What is that case we need to consider?
>> >
>> > Best regards,
>> > Seungwon Jeon
>>
>> This is different from unpacked requests handling since in the packed
>> err
>> check function you don't always return the error returned from
>> mmc_blk_err_check. In case the EXT_CSD_PACKED_INDEXED_ERROR is set you
>> return MMC_BLK_PARTIAL which is handled differently in the
>> mmc_blk_issue_rw_rd.
>> In our tests we set to 1 the packed bit in CMD23 arg of the first req
>> (in
>> the header). As a result, mmc_blk_err_check returned MMC_BLK_CMD_ERR.
>> However, mmc_blk_packed_err_check returned MMC_BLK_PARTIAL (since the
>> card
>> indicated the index of the first request as the failed request).
>> mmc_blk_issue_rw_rd handles MMC_BLK_PARTIAL by sending the packed
>> command
>> from the failed index and on, but since the packed bit was still set,
>> the
>> same error occurred and was handled the same way and we ended up with an
>> endless loop.
>> I hope my description is clear, let me know if you have further
>> questions.
> I tested your test case equally.
> Even though your test makes the header parameter incorrect artificially
> and keeps going with wrong setting repeatedly, we need to assure that
> the similar result can be found practically with normal running.
> I'll test it heavily and check more.
> And if you have more review about this version, please let me know.
>
> Thanks for your review.
> Seungwon Jeon.
Our code should be robust enough to deal with any card behavior.
Therefore, I think we need to avoid having endless loops regardless of the
scenario that caused it.
Currently I have no additional comments about this version.

Thanks,
Maya Erez
Consultant for Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum

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