Re: [PATCH v1 2/2] mmc: core: Allows to override the timeout value for ioctl() path

[Linus Walleij]

On Sun, Apr 24, 2022 at 12:16 AM Bean Huo <huobean@xxxxxxxxx> wrote:

> From: Bean Huo <beanhuo@xxxxxxxxxx>
>
> Occasionally, user-land applications initiate longer timeout values for certain commands
> through ioctl() system call. But so far we are still using a fixed timeout of 10 seconds
> in mmc_poll_for_busy() on the ioctl() path, even if a custom timeout is specified in the
> userspace application. This patch allows custom timeout values to override this default
> timeout values on the ioctl path.
>
> Cc: stable <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Bean Huo <beanhuo@xxxxxxxxxx>
(...)
>         if (idata->rpmb || (cmd.flags & MMC_RSP_R1B) == MMC_RSP_R1B) {
>                 /*
> -                * Ensure RPMB/R1B command has completed by polling CMD13
> -                * "Send Status".
> +                * Ensure RPMB/R1B command has completed by polling CMD13 "Send Status". Here we
> +                * allow to override the default timeout value if a custom timeout is specified.
>                  */
> -               err = mmc_poll_for_busy(card, MMC_BLK_TIMEOUT_MS, false,
> -                                       MMC_BUSY_IO);
> +               err = mmc_poll_for_busy(card, idata->ic.cmd_timeout_ms ? : MMC_BLK_TIMEOUT_MS,
> +                                       false, MMC_BUSY_IO);

I suppose it's OK (albeit dubious) that we have a userspace interface setting
a hardware-specific thing such as a timeout.

However: is MMC_BLK_TIMEOUT_MS even reasonable here? If you guys
know a better timeout for RPMB operations (from your experience)
what about defining MMC_RPMB_TIMEOUT_MS to something more
reasonable (and I suppose longer) and use that as fallback instead
of MMC_BLK_TIMEOUT_MS?

This knowledge (that RPMB commands can have long timeouts) is not
something that should be hidden in userspace.

Yours,
Linus Walleij