Re: [PATCH v1 2/2] mmc: sdhci: Use the SW timer when the HW timer cannot meet the timeout value required by the device

From: Adrian Hunter
Date: Fri Sep 24 2021 - 06:06:50 EST

On 24/09/21 12:17 pm, Bean Huo wrote:
> On Fri, 2021-09-24 at 08:29 +0300, Adrian Hunter wrote:
>>> If the data transmission timeout value required by the device
>>> exceeds
>>> the maximum timeout value of the host HW timer, we still use the HW
>>> timer with the maximum timeout value of the HW timer. This setting
>>> is
>>> suitable for most R/W situations. But sometimes, the device will
>>> complete
>>> the R/W task within its required timeout value (greater than the HW
>>> timer).
>>> In this case, the HW timer for data transmission will time out.
>>> Currently, in this condition, we disable the HW timer and use the
>>> SW
>>> timer only when the SDHCI_QUIRK2_DISABLE_HW_TIMEOUT quirk is set by
>>> the
>>> host driver. The patch is to remove this if statement restriction
>>> and
>>> allow data transmission to use the SW timer when the hardware timer
>>> cannot
>>> meet the required timeout value.
>> The reason it is a quirk is because it does not work for all
>> hardware.
>> For some controllers the timeout cannot really be disabled, only the
>> interrupt is disabled, and then the controller never indicates
>> completion
>> if the timeout is exceeded.
> Hi Adrian,
> Thanks for your review.
> Yes, you are right. But this quirk prevents disabling the hardware timeoutIRQ. The purpose of this patch is to disable the hardware timeout IRQ and
> select the software timeout.
> void __sdhci_set_timeout(struct sdhci_host *host, struct mmc_command
> *cmd)
> {
> bool too_big = false;
> u8 count = sdhci_calc_timeout(host, cmd, &too_big);
> if (too_big) {
> sdhci_calc_sw_timeout(host, cmd);
> sdhci_set_data_timeout_irq(host, false); // disable IRQ
> } else if (!(host->ier & SDHCI_INT_DATA_TIMEOUT)) {
> sdhci_set_data_timeout_irq(host, true);
> }
> sdhci_writeb(host, count, SDHCI_TIMEOUT_CONTROL);
> }
> The driver has detected that the hardware timer cannot meet the timeout
> requirements of the device, but we still use the hardware timer, which will
> allow potential timeout issuea . Rather than allowing a potential
> problem to exist, why can’t software timing be used to avoid this
> problem?

Timeouts aren't that accurate. The maximum is assumed still to work.
mmc->max_busy_timeout is used to tell the core what the maximum is.