Date:   Mon, 5 Aug 2019 09:33:21 +0200
From:   Ludovic BARRE <ludovic.barre@...com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     DTML <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Srinivas Kandagatla" <srinivas.kandagatla@...aro.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        <linux-stm32@...md-mailman.stormreply.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Linux-stm32] [PATCH V3 1/3] mmc: mmci: fix read status for busy
 detect

hi Ulf

On 7/26/19 11:41 AM, Ludovic BARRE wrote:
> hi Ulf
> 
> Thanks to your "Clarify comments ..." commit, like is closes
> I resumed upstream of this series.
> 
> On 7/15/19 6:31 PM, Ulf Hansson wrote:
>> On Mon, 3 Jun 2019 at 17:55, Ludovic Barre <ludovic.Barre@...com> wrote:
>>>
>>> From: Ludovic Barre <ludovic.barre@...com>
>>>
>>> "busy_detect_flag" is used to read & clear busy value of mmci status.
>>> "busy_detect_mask" is used to manage busy irq of mmci mask.
>>> So to read mmci status the busy_detect_flag must be take account.
>>> if the variant does not support busy detect feature the flag is null
>>> and there is no impact.
>>
>> By reading the changelog, it doesn't tell me the purpose of this
>> change. When going forward, please work harder on your changelogs.
>>
>> Make sure to answer the questions, *why* is this change needed,
>> *what/how* does the change do.
> 
> Ok, I will explain the differences with the legacy and the needs of 
> sdmmc variant about busy detection.
> 
>>
>>>
>>> Not need to re-read the status register in mmci_cmd_irq, the
>>> status parameter can be used.
>>>
>>> Signed-off-by: Ludovic Barre <ludovic.barre@...com>
>>> ---
>>>   drivers/mmc/host/mmci.c | 5 +++--
>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
>>> index 356833a..5b5cc45 100644
>>> --- a/drivers/mmc/host/mmci.c
>>> +++ b/drivers/mmc/host/mmci.c
>>> @@ -1240,7 +1240,7 @@ mmci_cmd_irq(struct mmci_host *host, struct 
>>> mmc_command *cmd,
>>>                   */
>>>                  if (!host->busy_status &&
>>>                      !(status & (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT)) &&
>>> -                   (readl(base + MMCISTATUS) & 
>>> host->variant->busy_detect_flag)) {
>>> +                   (status & host->variant->busy_detect_flag)) {
>>
>> I suggested you to do this change through some of my earlier comments,
>> however I think it should be made as a stand alone change.
>>
>> Anyway, when looking at the details in your series, I decided to try
>> to help out a bit, so I have prepared a couple of related patches for
>> cleaning up and clarifying the busy detection code/comments in mmci. I
>> have incorporated the above change, so let me post them asap.
>>
>>>
>>>                          /* Clear the busy start IRQ */
>>>                          writel(host->variant->busy_detect_mask,
>>> @@ -1517,7 +1517,8 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
>>>                   * to make sure that both start and end interrupts 
>>> are always
>>>                   * cleared one after the other.
>>>                   */
>>> -               status &= readl(host->base + MMCIMASK0);
>>> +               status &= readl(host->base + MMCIMASK0) |
>>> +                       host->variant->busy_detect_flag;
>>
>> As I told earlier in the review, this looks wrong to me.
>>
>> It means that you will add the bit for the ->busy_detect_flag to the
>> status field we have just read from the MMCISTATUS register. That
>> means the busy status may be set when it shouldn't.
>>
>>>                  if (host->variant->busy_detect)
>>>                          writel(status & 
>>> ~host->variant->busy_detect_mask,
>>>                                 host->base + MMCICLEAR);
>>> -- 
>>> 2.7.4
>>>
>>
>> By looking at the other changes in the series, I assume @subject patch
>> is intended to prepare for the other changes on top. But it's not
>> really clear.
>>
>> Anyway, in that regards, the below is my observations of what seems to
>> be important part, when supporting busy detection for the stm32 sdmmc
>> variant (except the timeout things in patch2, which I intend to
>> comment separately on).
>>
>> I figured, these are the involved register bits/masks:
>>
>> MMCISTATUS:
>> MCI_STM32_BUSYD0 BIT(20)
>> MCI_STM32_BUSYD0END BIT(21)
>>
>> MMCIMASK0:
>> MCI_STM32_BUSYD0ENDMASK BIT(21)
> 
> it's exact:
> MCI_STM32_BUSYD0 BIT(20): This is a hardware status flag only (inverted 
> value of d0 line), it does not generate an interrupt, and so no mask
> bit.
> 
> MCI_STM32_BUSYD0ENDMASK BIT(21): This indicates only end of busy
> following a CMD response. On busy to Not busy changes, an interrupt
> is generated (if unmask) and BUSYD0END status flag is set.
> status flag is cleared by writing corresponding interrupt clear bit in 
> MMCICLEAR.
> 
>>
>> For the legacy ST variant, there is only one register bit in
>> MMCISTATUS that is used for indicating busy (MCI_ST_CARDBUSY BIT(24)).
>> There is no dedicated busy-end bit for the busy-end IRQ, which I
>> believe is the reason to why the current code also is bit messy.
> 
> yes
> 
>>
>> It seems like the stm32 sdmmc variant have a separate status bit for
>> the busy-end IRQ, correct?
> 
> yes
> 
>>
>> If I understand correctly by looking at patch3, you don't use the
>> dedicated busy-end status bit (MCI_STM32_BUSYD0END), right? Then why
>> not?
> 
> like your are clarify in previous series, the busy detection is done
> in 3 steps.
> 
> if I use:
> .busy_detect_flag    = MCI_STM32_BUSYD0ENDMASK,
> .busy_detect_mask    = MCI_STM32_BUSYD0ENDMASK,
> 
> the sdmmc request will be not correctly completed, because the third 
> step can't be happen.
> 
> chronologies:
> step1: when busyd0end change to 1
>   => busyd0end interrupt is unmasked
>   => busy_status = cmd_sent | respend
>   => return to mmci_irq
> step2: busyd0end is yet to 1
>   => clear the busyd0end interrupt
>      => the hardware clear busyd0end status flag on interrupt clear
>   => return to mmci_irq
> 
> like MCI_STM32_BUSYD0END interrupt is generated only on change
> busy to not busy, when the interrupt is cleared (status is 0)
> the step 3 can't happen (no irq pending to re-enter in mmci_cmd_irq).
> sdmmc can't complete the request.
> 
> If I use:
> .busy_detect_flag    = MCI_STM32_BUSYD0,
> .busy_detect_mask    = MCI_STM32_BUSYD0ENDMASK,
> 
> Like there is no MCI_STM32_BUSYD0 irq mask, the status read in mmci_irq
> "status &= readl(host->base + MMCIMASK0)" can't take account the 
> busy_detect_flag (for sdmmc). So the  step 2 can't be passed.
> However we could share re-read between step 1 and step 2.
> 
> proposal:
> 
> +
> +        u32 busy_val = readl(base + MMCISTATUS) &
> +            host->variant->busy_detect_flag;
> +
>           if (!host->busy_status &&
> -            !(status & (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT)) &&
> -            (readl(base + MMCISTATUS) & 
> host->variant->busy_detect_flag)) {
> +            !(status & (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT)) && busy_val) {
> 
>               writel(readl(base + MMCIMASK0) |
>                      host->variant->busy_detect_mask,
> @@ -1262,8 +1265,7 @@ mmci_cmd_irq(struct mmci_host *host, struct 
> mmc_command *cmd,
>            * both the start and the end interrupts needs to be cleared,
>            * one after the other. So, clear the busy start IRQ here.
>            */
> -        if (host->busy_status &&
> -            (status & host->variant->busy_detect_flag)) {
> +        if (host->busy_status && busy_val) {
> 
> 
> what do you think about it ?
> 

I give up this proposal for a new version based on mmci_host_ops
callback to done the busy completion.

>>
>> Thoughts?
>>
>> Kind regards
>> Uffe
>>
> 
> Regards
> Ludo
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