Re: [PATCH v3 2/5] mmc: core: API for temporarily disabling auto-retuning due to errors

[Ulf Hansson <ulf.hansson@linaro.org>]

On Sat, 8 Jun 2019 at 00:37, Douglas Anderson <dianders@chromium.org> wrote:
>
> Normally when the MMC core sees an "-EILSEQ" error returned by a host
> controller then it will trigger a retuning of the card.  This is
> generally a good idea.
>
> However, if a command is expected to sometimes cause transfer errors
> then these transfer errors shouldn't cause a re-tuning.  This
> re-tuning will be a needless waste of time.  One example case where a
> transfer is expected to cause errors is when transitioning between
> idle (sometimes referred to as "sleep" in Broadcom code) and active
> state on certain Broadcom WiFi cards.  Specifically if the card was
> already transitioning between states when the command was sent it
> could cause an error on the SDIO bus.
>
> Let's add an API that the SDIO card drivers can call that will
> temporarily disable the auto-tuning functionality.  Then we can add a
> call to this in the Broadcom WiFi driver and any other driver that
> might have similar needs.
>
> NOTE: this makes the assumption that the card is already tuned well
> enough that it's OK to disable the auto-retuning during one of these
> error-prone situations.  Presumably the driver code performing the
> error-prone transfer knows how to recover / retry from errors.  ...and
> after we can get back to a state where transfers are no longer
> error-prone then we can enable the auto-retuning again.  If we truly
> find ourselves in a case where the card needs to be retuned sometimes
> to handle one of these error-prone transfers then we can always try a
> few transfers first without auto-retuning and then re-try with
> auto-retuning if the first few fail.
>
> Without this change on rk3288-veyron-minnie I periodically see this in
> the logs of a machine just sitting there idle:
>   dwmmc_rockchip ff0d0000.dwmmc: Successfully tuned phase to XYZ
>
> Fixes: bd11e8bd03ca ("mmc: core: Flag re-tuning is needed on CRC errors")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> Note that are are a whole boatload of different ways that we could
> provide an API for the Broadcom WiFi SDIO driver.  This patch
> illustrates one way but if maintainers feel strongly that this is too
> ugly and have a better idea then I can give it a shot too.  From a
> purist point of view I kinda felt that the "expect errors" really
> belonged as part of the mmc_request structure, but getting it into
> there meant changing a whole pile of core SD/MMC APIs.  Simply adding
> it to the host seemed to match the current style better and was a less
> intrusive change.
>
> Changes in v3:
> - Took out the spinlock since I believe this is all in one context.

This needs to be clarified, preferable also in a function header.

If I understand correctly, the SDIO func driver needs the host to be
claimed when it calls mmc_expect_errors_begin(). More importantly, it
also needs to be keep it claimed until after it had called
mmc_expect_errors_end(). Correct?

>
> Changes in v2:
> - Updated commit message to clarify based on discussion of v1.
>
>  drivers/mmc/core/core.c  | 19 +++++++++++++++++--
>  include/linux/mmc/core.h |  2 ++
>  include/linux/mmc/host.h |  1 +
>  3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 6db36dc870b5..bc109ec49406 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -144,8 +144,9 @@ void mmc_request_done(struct mmc_host *host, struct mmc_request *mrq)
>         int err = cmd->error;
>
>         /* Flag re-tuning needed on CRC errors */
> -       if ((cmd->opcode != MMC_SEND_TUNING_BLOCK &&
> -           cmd->opcode != MMC_SEND_TUNING_BLOCK_HS200) &&
> +       if (cmd->opcode != MMC_SEND_TUNING_BLOCK &&
> +           cmd->opcode != MMC_SEND_TUNING_BLOCK_HS200 &&
> +           !host->expect_errors &&
>             (err == -EILSEQ || (mrq->sbc && mrq->sbc->error == -EILSEQ) ||
>             (mrq->data && mrq->data->error == -EILSEQ) ||
>             (mrq->stop && mrq->stop->error == -EILSEQ)))
> @@ -2163,6 +2164,20 @@ int mmc_sw_reset(struct mmc_host *host)
>  }
>  EXPORT_SYMBOL(mmc_sw_reset);
>
> +void mmc_expect_errors_begin(struct mmc_host *host)
> +{
> +       WARN_ON(host->expect_errors);

Please remove the WARN_ON. If you believe there is a need for
reference counting, then please add that instead (but likely not in
the phase?).

> +       host->expect_errors = true;
> +}
> +EXPORT_SYMBOL_GPL(mmc_expect_errors_begin);
> +
> +void mmc_expect_errors_end(struct mmc_host *host)
> +{
> +       WARN_ON(!host->expect_errors);

Ditto.

> +       host->expect_errors = false;
> +}
> +EXPORT_SYMBOL_GPL(mmc_expect_errors_end);

These new APIs seems to be useful solely for SDIO. Even if it turns
out later that they can be made generic, I suggest to start with a
SDIO func API instead.

However, using a new host variable (->expect_errors) is fine by me.

> +
>  static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
>  {
>         host->f_init = freq;
> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
> index 134a6483347a..02a13abf0cda 100644
> --- a/include/linux/mmc/core.h
> +++ b/include/linux/mmc/core.h
> @@ -178,6 +178,8 @@ int mmc_wait_for_cmd(struct mmc_host *host, struct mmc_command *cmd,
>
>  int mmc_hw_reset(struct mmc_host *host);
>  int mmc_sw_reset(struct mmc_host *host);
> +void mmc_expect_errors_begin(struct mmc_host *host);
> +void mmc_expect_errors_end(struct mmc_host *host);

The API prevents a new re-tune to be "scheduled" in case requests are
failing with -EILSEQ.

To better reflect that, may I suggest to rename this to
sdio_retune_crc_disable() and sdio_retune_crc_enable(). Or something
along those lines.


>  void mmc_set_data_timeout(struct mmc_data *data, const struct mmc_card *card);
>
>  #endif /* LINUX_MMC_CORE_H */
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 43d0f0c496f6..8d553fb8c834 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -398,6 +398,7 @@ struct mmc_host {
>         unsigned int            retune_now:1;   /* do re-tuning at next req */
>         unsigned int            retune_paused:1; /* re-tuning is temporarily disabled */
>         unsigned int            use_blk_mq:1;   /* use blk-mq */
> +       unsigned int            expect_errors:1; /* don't trigger retune upon errors */
>
>         int                     rescan_disable; /* disable card detection */
>         int                     rescan_entered; /* used with nonremovable devices */
> --
> 2.22.0.rc2.383.gf4fbbf30c2-goog
>

Kind regards
Uffe