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

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Date:   Mon, 14 Mar 2022 17:20:55 +0800
From:   Michael Wu <michael@...winnertech.com>
To:     Adrian Hunter <adrian.hunter@...el.com>, ulf.hansson@...aro.org,
        avri.altman@....com, beanhuo@...ron.com, porzio@...il.com
Cc:     linux-mmc@...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 14/03/2022 14:54, Adrian Hunter wrote:
> On 12/03/2022 06:43, Michael Wu wrote:
>> 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.
>>
> 
> Fixes tag?
> 

Hi Adrian,
My patch intend to fix the cache problem brought by the following two 
patches:

Fixes: d0c97cfb81ebc ("mmc: core: Use CMD23 for multiblock transfers 
when we can.")
Fixes: e9d5c746246c8 ("mmc/block: switch to using blk_queue_write_cache()")

I'm not sure if this is what you referred to ("Fixes tag"). Please 
correct me if I misunderstood.

>> Signed-off-by: Michael Wu <michael@...winnertech.com>
>> ---
>>   drivers/mmc/core/block.c | 20 ++++++++++++++------
>>   1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
>> index 689eb9afeeed..1e508c079c1e 100644
>> --- a/drivers/mmc/core/block.c
>> +++ b/drivers/mmc/core/block.c
>> @@ -2279,6 +2279,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>>   	struct mmc_blk_data *md;
>>   	int devidx, ret;
>>   	char cap_str[10];
>> +	bool enable_cache = false;
>> +	bool enable_fua = false;
>>   
>>   	devidx = ida_simple_get(&mmc_blk_ida, 0, max_devices, GFP_KERNEL);
>>   	if (devidx < 0) {
>> @@ -2375,12 +2377,18 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>>   			md->flags |= MMC_BLK_CMD23;
>>   	}
>>   
>> -	if (mmc_card_mmc(card) &&
>> -	    md->flags & MMC_BLK_CMD23 &&
>> -	    ((card->ext_csd.rel_param & EXT_CSD_WR_REL_PARAM_EN) ||
>> -	     card->ext_csd.rel_sectors)) {
>> -		md->flags |= MMC_BLK_REL_WR;
>> -		blk_queue_write_cache(md->queue.queue, true, true);
>> +	if (mmc_card_mmc(card)) {
>> +		if (md->flags & MMC_BLK_CMD23 &&
>> +			((card->ext_csd.rel_param & EXT_CSD_WR_REL_PARAM_EN) ||
>> +			card->ext_csd.rel_sectors)) {
>> +			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);
>>   	}
> 
> Seems like we should inform block layer about SD card cache also
> 

I saw another mail by Avri Altman, which says few days will be needed to 
ask internally. Shall I wait or make another change here on 'inform 
block layer about SD card cache'?

>>   
>>   	string_get_size((u64)size, 512, STRING_UNITS_2,

-- 
Best Regards,
Michael Wu