linux-kernel - Re: [PATCH] mmc: sdhci-cadence: send tune request twice to work around errata

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Date:   Wed, 4 Apr 2018 18:05:42 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Piotr Sroka <piotrs@...ence.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] mmc: sdhci-cadence: send tune request twice to work
 around errata

Hi.

2018-04-04 16:35 GMT+09:00 Ulf Hansson <ulf.hansson@...aro.org>:
> On 27 March 2018 at 11:29, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> Cadence sent out an errata report to their customers of this IP.
>> This errata is not so severe, but the tune request should be sent
>> twice to avoid the potential issue.
>>
>> Quote from the report:
>>
>> Problem Summary
>> ---------------
>> The IP6116 SD/eMMC PHY design has a timing issue on receive data path.
>> This issue may lead to an incorrect values of read/write pointers of
>> the synchronization FIFO. Such a situation can happen at the SDR104
>> and HS200 tuning procedure when the PHY is requested to change a phase
>> of sampling clock when moving to the next tuning iteration.
>>
>> Workarounds
>> -----------
>> The following are valid workarounds to resolve the issue:
>>
>> 1. In eMMC mode, software sends tune request twice instead of once at
>>    each iteration. This means that the clock phase is not changed on
>>    the second request so there is no potential for clock instability.
>> 2. In SD mode, software must not use the hardware tuning and instead
>>    perform an almost identical procedure to eMMC, using the HRS34 Tune
>>    Force register.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>
> Do you want this to be tagged for stable as well? And perhaps you
> could add a fixes tag?


It would be nicer to make it a back-port candidate,
but this patch can not cleanly apply to the initial commit of this driver.


If you apply it for -next, it would be fine with me.






-- 
Best Regards
Masahiro Yamada