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

Adrian Hunter
2022-03-16T16:08:55Z

On 16.3.2022 16.46, Christian Löhle wrote:
>> So we are not going to let the block layer know about SD cache?
>> Or is it a separate change?
>
> I have some code for this laying around, but as it requires reading, parsing and writing Function Registers,
> in particular PEH, it's a lot of boilerplate code to get the functionality, but I'll clean it up and send a patch in the coming weeks.
>

We have the sd cache flush. We would presumably just need to call blk_queue_write_cache()
for the !mmc_card_mmc(card) case e.g.

if (mmc_has_reliable_write(card)) {
md->flags |= MMC_BLK_REL_WR;
enable_fua = true;
}

if (mmc_cache_enabled(card->host))
enable_cache = true;

blk_queue_write_cache(md->queue.queue, enable_cache, enable_fua);

Avri, were you objecting to that?

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> From: Adrian Hunter <adrian.hunter@intel.com>
> Sent: Wednesday, March 16, 2022 12:28 PM
> To: Avri Altman; Michael Wu; ulf.hansson@linaro.org; beanhuo@micron.com; porzio@gmail.com
> Cc: linux-mmc@vger.kernel.org; linux-kernel@vger.kernel.org; allwinner-opensource-support
> Subject: Re: [PATCH] mmc: block: enable cache-flushing when mmc cache is on
>
> On 16.3.2022 13.09, Avri Altman wrote:
>>> Hi Avril & Adrian,
>>> Thanks for your efforts. Could we have an agreement now --
>>>
>>> 1. enabling-cache and cmd23/reliable-write should be independent;
>>>
>>> Here's what I found in the spec JESD84-B51:
>>>   > 6.6.31 Cache
>>>   > Caching of data shall apply only for the single block
>>>   > read/write(CMD17/24), pre-defined multiple block
>>>   > read/write(CMD23+CMD18/25) and open ended multiple block
>>>   > read/write(CMD18/25+CMD12) commands and excludes any other access
>>>   > e.g., to the register space(e.g., CMD6).
>>> Which means with CMD18/25+CMD12 (without using CMD23), the cache can
>>> also be enabled. Maybe this could be an evidence of the independence
>>> between enabling-cache and cmd23/reliable-write?
>> Acked-by: Avri Altman <avri.altman@wdc.com>
>>
>> Thanks,
>> Avri
>>
>>>
>>> 2. We don't consider supporting SD in this change.
>>>
>>>   > On 14/03/2022 19:10, Avri Altman wrote:
>>>   >> Here is what our SD system guys wrote:
>>>   >> " In SD we don’t support reliable write and this eMMC driver may not
>>>   >>    be utilizing the cache feature we added in SD5.0.
>>>   >>   The method of cache flush is different between SD and eMMC."
>>>   >>
>>>   >> So adding SD seems to be out of scope of this change.
>>>
>>> Is there anything else I can do about this patch? Thanks again.
>
> So we are not going to let the block layer know about SD cache?
> Or is it a separate change?
> =
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