linux-kernel - Re: [PATCH] mmc: block: enable cache-flushing when mmc cache is on

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Message-ID: <4436fbb9-32fa-82f0-bf99-344b9bfddf78@intel.com>
Date:   Mon, 14 Mar 2022 12:32:45 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Avri Altman <Avri.Altman@....com>,
        Michael Wu <michael@...winnertech.com>, ulf.hansson@...aro.org,
        beanhuo@...ron.com, porzio@...il.com
Cc:     lixiang <lixiang@...winnertech.com>, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: block: enable cache-flushing when mmc cache is on

On 14/03/2022 09:26, Avri Altman wrote:
> Hi,
>> The mmc core enable cache on default. But it only enables cache-flushing
>> when host supports cmd23 and eMMC supports reliable write.
>> For hosts which do not support cmd23 or eMMCs which do not support
>> reliable write, the cache can not be flushed by `sync` command.
>> This may leads to cache data lost.
>> This patch enables cache-flushing as long as cache is enabled, no matter host
>> supports cmd23 and/or eMMC supports reliable write or not.
> I looked in the spec and indeed couldn't find why enabling cache is dependent of cmd23/reliable write.
> Nor I was able to find the original commit log.

Reliable write was added first, so it might have been an oversight:

commit 881d1c25f765938a95def5afe39486ce39f9fc96
Author: Seungwon Jeon <tgih.jun@...sung.com>
Date:   Fri Oct 14 14:03:21 2011 +0900

    mmc: core: Add cache control for eMMC4.5 device
    
    This patch adds cache feature of eMMC4.5 Spec.
    If device supports cache capability, host can utilize some specific
    operations.
    
    Signed-off-by: Seungwon Jeon <tgih.jun@...sung.com>
    Signed-off-by: Jaehoon Chung <jh80.chung@...sung.com>
    Signed-off-by: Chris Ball <cjb@...top.org>



> 
> Please allow few days to ask internally.
> 
> Thanks,
> Avri