linux-kernel - Re: [PATCH V3 1/3] mmc: core: Add partial initialization support

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Message-ID: <b59331a1-567f-403c-9173-b0919bdd0f8e@quicinc.com>
Date: Mon, 29 Jan 2024 12:20:11 +0530
From: Sarthak Garg <quic_sartgarg@...cinc.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
CC: Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Adrian Hunter
	<adrian.hunter@...el.com>, <linux-mmc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <quic_cang@...cinc.com>, <quic_nguyenb@...cinc.com>,
        <quic_rampraka@...cinc.com>, <quic_pragalla@...cinc.com>,
        <quic_sayalil@...cinc.com>, <quic_nitirawa@...cinc.com>,
        <quic_sachgupt@...cinc.com>, <quic_bhaskarv@...cinc.com>,
        <quic_narepall@...cinc.com>, <kernel@...cinc.com>,
        Veerabhadrarao Badiganti
	<quic_vbadigan@...cinc.com>
Subject: Re: [PATCH V3 1/3] mmc: core: Add partial initialization support



On 10/27/2023 3:23 PM, Ulf Hansson wrote:
> [...]
> 
>>>> +{
>>>> +       int err = 0;
>>>> +       struct mmc_card *card = host->card;
>>>> +
>>>> +       mmc_set_bus_width(host, host->cached_ios.bus_width);
>>>> +       mmc_set_timing(host, host->cached_ios.timing);
>>>> +       if (host->cached_ios.enhanced_strobe) {
>>>> +               host->ios.enhanced_strobe = true;
>>>> +               if (host->ops->hs400_enhanced_strobe)
>>>> +                       host->ops->hs400_enhanced_strobe(host, &host->ios);
>>>> +       }
>>>> +       mmc_set_clock(host, host->cached_ios.clock);
>>>> +       mmc_set_bus_mode(host, host->cached_ios.bus_mode);
>>>> +
>>>
>>> Rather than re-using the above APIs and the ->set_ios() callback in
>>> the host, I believe it would be better to add a new host ops to manage
>>> all of the above at once instead. Something along the lines of the
>>> below, would then replace all of the above.
>>>
>>> host->ops->restore_ios(host, &host->cached_ios)
>>> memcpy(&host->ios, &host->cached_ios, sizeof(host->ios));
>>>
>>> Would that make sense to you too?
>>>
>>
>>
>> I didn't get this completely. Do you mean that we should implement a new
>> restore_ios callback (e.g. sdhci_restore_ios) similar to sdhci_set_ios
>> and removing all the redundant code from sdhci_set_ios which should
>> achieve the behaviour same as calling all the above mmc_set_* API's ?
> 
> Correct. Would it not simply the things in the driver too?
> 
>>
>>
>>>> +       if (!mmc_card_hs400es(card) &&
>>>> +                       (mmc_card_hs200(card) || mmc_card_hs400(card))) {
>>>> +               err = mmc_execute_tuning(card);
>>>> +               if (err) {
>>>> +                       pr_err("%s: %s: Tuning failed (%d)\n",
>>>> +                               mmc_hostname(host), __func__, err);
>>>
>>> There is already a print being done in mmc_execute_tuning() at
>>> failure. So, let's drop the above print.
>>>
>>
>> Sure will take care in V4.
>>
>>>> +                       goto out;
>>>> +               }
>>>> +       }
>>>> +
>>>> +       err = mmc_test_awake_ext_csd(host);
>>>
>>> Again, I don't get why this is needed, so let's discuss this more.
>>>
>>
>> This is just a safety check added because ext_csd has some W/E_P or
>> W/C_P registers which gets reset if any HW reset happens to the card.
>> So this will check for those cases if any other vendor is doing reset as
>> part of suspend and compare a subset of those W/E_P and W/C_P registers
>> and if they are changed then we will bail out of this partial init
>> feature and go for full initialization.
>> We are also fine with removing this function but just added for the
>> above mentioned case.
> 
> In that case, I would rather remove it as I think it's superfluous.
> 
> More precisely, I would expect that we fail to wake up the card with a
> CMD5 (get an error response for the CMD) if there has been a HW reset
> somewhere done before.
> 
> Another reason to *not* read the ext_csd would be to further improve
> the resume time, as reading it takes time too. I would be curious to
> know how much though. :-)
> 
> [...]
> 
> Kind regards
> Uffe

Hi ulf,

Sorry for the delay but we are seeing some stability issues when testing 
this feature with HS400 cards which I am debugging and may take some 
time and will come back.
Note: This feature is working perfectly fine with HS400ES cards.