linux-kernel - Re: [PATCH] mmc: core: Improve fallback to speed modes if eMMC HS200 fails

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Message-ID: <ece53010-b7ed-6b12-1baa-08505537854d@gmail.com>
Date:   Mon, 14 Mar 2022 23:02:37 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, Adrian Hunter <adrian.hunter@...el.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Yann Gautier <yann.gautier@...s.st.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: core: Improve fallback to speed modes if eMMC HS200
 fails

On 14.03.2022 11:54, Ulf Hansson wrote:
> On Thu, 3 Mar 2022 at 17:45, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>
>> In the error path of mmc_select_hs200() we are trying our best to restore
>> the card/host into a valid state. This makes sense, especially if we
>> encounter a simple switch error (-EBADMSG). However, rather than then
>> continue with using the legacy speed mode, let's try the other better speed
>> modes first. Additionally, let's update the card->mmc_avail_type to avoid
>> us from trying a broken HS200 mode again.
>>
>> In an Amlogic S905W based TV box where the switch to HS200 mode fails for
>> the eMMC, this allows us to use the eMMC in DDR mode in favor of the legacy
>> mode, which greatly improves the performance.
>>
>> Suggested-by: Heiner Kallweit <hkallweit1@...il.com>
>> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> 
> Heiner, does this solve your problems? Can you perhaps run some tests
> at your side to see how it works for you?
> 

Tested-by: Heiner Kallweit <hkallweit1@...il.com>

> Kind regards
> Uffe
> 
Heiner

>> ---
>>  drivers/mmc/core/mmc.c | 16 +++++++++++++---
>>  1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index 141f851c9f58..6e7db45cb8e0 100644
>> --- a/drivers/mmc/core/mmc.c
>> +++ b/drivers/mmc/core/mmc.c
>> @@ -1518,13 +1518,23 @@ static int mmc_select_timing(struct mmc_card *card)
>>         if (!mmc_can_ext_csd(card))
>>                 goto bus_speed;
>>
>> -       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES)
>> +       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES) {
>>                 err = mmc_select_hs400es(card);
>> -       else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200)
>> +               goto out;
>> +       }
>> +
>> +       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200) {
>>                 err = mmc_select_hs200(card);
>> -       else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS)
>> +               if (err == -EBADMSG)
>> +                       card->mmc_avail_type &= ~EXT_CSD_CARD_TYPE_HS200;
>> +               else
>> +                       goto out;
>> +       }
>> +
>> +       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS)
>>                 err = mmc_select_hs(card);
>>
>> +out:
>>         if (err && err != -EBADMSG)
>>                 return err;
>>
>> --
>> 2.25.1
>>