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

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Message-ID: <a1230f11-a2dd-1959-5444-28c57d3babf6@intel.com>
Date:   Wed, 16 Mar 2022 18:05:52 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Christian Löhle <CLoehle@...erstone.com>,
        Avri Altman <Avri.Altman@....com>,
        Michael Wu <michael@...winnertech.com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "porzio@...il.com" <porzio@...il.com>
Cc:     "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        allwinner-opensource-support 
        <allwinner-opensource-support@...winnertech.com>
Subject: Re: [PATCH] mmc: block: enable cache-flushing when mmc cache is on

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?

> 
> 
> 
> 
> From: Adrian Hunter <adrian.hunter@...el.com>
> Sent: Wednesday, March 16, 2022 12:28 PM
> To: Avri Altman; Michael Wu; ulf.hansson@...aro.org; beanhuo@...ron.com; porzio@...il.com
> Cc: linux-mmc@...r.kernel.org; linux-kernel@...r.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@....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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