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SubjectRe: [PATCH 1/4] mmc: mmci: avoid fake busy polling
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hi Ulf

On 4/23/19 3:39 PM, Ulf Hansson wrote:
> On Tue, 5 Mar 2019 at 17:10, Ludovic Barre <ludovic.Barre@st.com> wrote:
>>
>> From: Ludovic Barre <ludovic.barre@st.com>
>>
>> The busy status bit could occurred even if no busy response is
>> expected (example cmd11). On sdmmc variant, the busy_detect_flag
>> reflects inverted value of d0 state, it's sampled at the end of a
>> CMD response and a second time 2 clk cycles after the CMD response.
>> To avoid a fake busy, the busy status could be checked and polled
>> only if the command has RSP_BUSY flag.
>
> I would appreciate a better explanation of what this patch really changes.
>
> The above is giving some background to the behavior of sdmmc variant,
> but at this point that variant doesn't even have the
> ->variant->busy_detect flag set.
>

Yes, I will try to explain more and focus on common behavior.

>>
>> Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
>> ---
>> drivers/mmc/host/mmci.c | 19 +++++++++++++------
>> 1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
>> index 387ff14..4901b73 100644
>> --- a/drivers/mmc/host/mmci.c
>> +++ b/drivers/mmc/host/mmci.c
>> @@ -1220,12 +1220,13 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
>> unsigned int status)
>> {
>> void __iomem *base = host->base;
>> - bool sbc;
>> + bool sbc, busy_resp;
>>
>> if (!cmd)
>> return;
>>
>> sbc = (cmd == host->mrq->sbc);
>> + busy_resp = !!(cmd->flags & MMC_RSP_BUSY);
>>
>> /*
>> * We need to be one of these interrupts to be considered worth
>> @@ -1239,8 +1240,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
>> /*
>> * ST Micro variant: handle busy detection.
>> */
>> - if (host->variant->busy_detect) {
>> - bool busy_resp = !!(cmd->flags & MMC_RSP_BUSY);
>> + if (busy_resp && host->variant->busy_detect) {
>>
>> /* We are busy with a command, return */
>> if (host->busy_status &&
>> @@ -1253,7 +1253,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
>> * that the special busy status bit is still set before
>> * proceeding.
>> */
>> - if (!host->busy_status && busy_resp &&
>> + if (!host->busy_status &&
>> !(status & (MCI_CMDCRCFAIL|MCI_CMDTIMEOUT)) &&
>> (readl(base + MMCISTATUS) & host->variant->busy_detect_flag)) {
>
> All the changes above makes perfect sense to me, but looks more like a
> cleanup of the code, rather than actually changing the behavior.

yes, few changing (this just avoid to enter in
"if (host->variant->busy_detect)") at each time.
I could move this part in cleanup patch (before this patch)

>
>>
>> @@ -1508,6 +1508,7 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
>> {
>> struct mmci_host *host = dev_id;
>> u32 status;
>> + bool busy_resp;
>> int ret = 0;
>>
>> spin_lock(&host->lock);
>> @@ -1550,9 +1551,15 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
>> }
>>
>> /*
>> - * Don't poll for busy completion in irq context.
>> + * Don't poll for:
>> + * -busy completion in irq context.
>> + * -no busy response expected.
>> */
>> - if (host->variant->busy_detect && host->busy_status)
>> + busy_resp = host->cmd ?
>> + !!(host->cmd->flags & MMC_RSP_BUSY) : false;
>
> This doesn't make sense to me, but I may be missing something.
>
> host->busy_status is being updated by mmci_cmd_irq() and only when
> MMC_RSP_BUSY is set for the command in flight. In other words,
> checking for MMC_RSP_BUSY here as well is redundant. No?

In mmci_irq the "do while" loops until the status is totally cleared.

Today (for variant with busy_detect option), the status busy_detect_flag
is excluded only while busy_status period (command with MMC_RSP_BUSY and
while busy line is low => "busy_status=1")

On SDMMC variant I noticed that busy_detect_flag status could be enabled
even if the command is not MMC_RSP_BUSY, for example sdmmc variant stay
in loop while cmd11 voltage switch.

So I wish extend host->variant->busy_detect_flag exclusion for all
commands which is not a MMC_RSP_BUSY. I suppose that other variants
could have the same behavior, and else there is no impact, normally.

>
>> +
>> + if (host->variant->busy_detect &&
>> + (!busy_resp || host->busy_status))
>> status &= ~host->variant->busy_detect_flag;
>>
>> ret = 1;
>> --
>> 2.7.4
>>
>
> Kind regards
> Uffe
>

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