RE: [PATCH v2] mmc: core: Add support for cache ctrl for SD cards

[Avri Altman]

> In SD spec v6.x the SD function extension registers for performance
> enhancements were introduced. As a part of this an optional internal cache
> on the SD card, can be used to improve performance.
> 
> The let the SD card use the cache, the host needs to enable it and manage
> flushing of the cache, so let's add support for this.
> 
> Note that for an SD card supporting the cache it's mandatory for it, to
> also support the poweroff notification feature. According to the SD spec,
> if the cache has been enabled and a poweroff notification is sent to the
> card, that implicitly also means that the card should flush its internal
> cache. Therefore, dealing with cache flushing for REQ_OP_FLUSH block
> requests is sufficient.
> 
> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Reviewed-by: Avri Altman <avri.altman@xxxxxxx>

> ---
> 
> Changes in v2:
>  - Converted to use the BIT() macro for clarification, as suggested by Linus.
>  - Reset SD_EXT_PERF_CACHE bit when cache enable fails, as suggested by
> Avri.
> 
> Note that:
>  - I decided to keep the error path when failing to enable the cache. It's
> seems more robust, as it's unclear what happens with the SD card at failure.
> Additionally, if improvements are needed we can make it on top.
> 
> ---
>  drivers/mmc/core/mmc_ops.c |   1 +
>  drivers/mmc/core/mmc_ops.h |   1 +
>  drivers/mmc/core/sd.c      | 100
> +++++++++++++++++++++++++++++++++++++
>  include/linux/mmc/card.h   |   1 +
>  4 files changed, 103 insertions(+)
> 
> diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
> index af423acc4c88..3c58f6d0f482 100644
> --- a/drivers/mmc/core/mmc_ops.c
> +++ b/drivers/mmc/core/mmc_ops.c
> @@ -456,6 +456,7 @@ static int mmc_busy_cb(void *cb_data, bool *busy)
>                 err = R1_STATUS(status) ? -EIO : 0;
>                 break;
>         case MMC_BUSY_HPI:
> +       case MMC_BUSY_EXTR_SINGLE:
>                 break;
>         default:
>                 err = -EINVAL;
> diff --git a/drivers/mmc/core/mmc_ops.h b/drivers/mmc/core/mmc_ops.h
> index c3c1d9c2577e..41ab4f573a31 100644
> --- a/drivers/mmc/core/mmc_ops.h
> +++ b/drivers/mmc/core/mmc_ops.h
> @@ -14,6 +14,7 @@ enum mmc_busy_cmd {
>         MMC_BUSY_CMD6,
>         MMC_BUSY_ERASE,
>         MMC_BUSY_HPI,
> +       MMC_BUSY_EXTR_SINGLE,
>  };
> 
>  struct mmc_host;
> diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> index bd40c682d264..781c1e24308c 100644
> --- a/drivers/mmc/core/sd.c
> +++ b/drivers/mmc/core/sd.c
> @@ -67,6 +67,7 @@ static const unsigned int sd_au_size[] = {
>         })
> 
>  #define SD_POWEROFF_NOTIFY_TIMEOUT_MS 2000
> +#define SD_WRITE_EXTR_SINGLE_TIMEOUT_MS 1000
> 
>  struct sd_busy_data {
>         struct mmc_card *card;
> @@ -1287,6 +1288,96 @@ static int sd_read_ext_regs(struct mmc_card
> *card)
>         return err;
>  }
> 
> +static bool sd_cache_enabled(struct mmc_host *host)
> +{
> +       return host->card->ext_perf.feature_enabled & SD_EXT_PERF_CACHE;
> +}
> +
> +static int sd_flush_cache(struct mmc_host *host)
> +{
> +       struct mmc_card *card = host->card;
> +       u8 *reg_buf, fno, page;
> +       u16 offset;
> +       int err;
> +
> +       if (!sd_cache_enabled(host))
> +               return 0;
> +
> +       reg_buf = kzalloc(512, GFP_KERNEL);
> +       if (!reg_buf)
> +               return -ENOMEM;
> +
> +       /*
> +        * Set Flush Cache at bit 0 in the performance enhancement register at
> +        * 261 bytes offset.
> +        */
> +       fno = card->ext_perf.fno;
> +       page = card->ext_perf.page;
> +       offset = card->ext_perf.offset + 261;
> +
> +       err = sd_write_ext_reg(card, fno, page, offset, BIT(0));
> +       if (err) {
> +               pr_warn("%s: error %d writing Cache Flush bit\n",
> +                       mmc_hostname(host), err);
> +               goto out;
> +       }
> +
> +       err = mmc_poll_for_busy(card,
> SD_WRITE_EXTR_SINGLE_TIMEOUT_MS, false,
> +                               MMC_BUSY_EXTR_SINGLE);
> +       if (err)
> +               goto out;
> +
> +       /*
> +        * Read the Flush Cache bit. The card shall reset it, to confirm that
> +        * it's has completed the flushing of the cache.
> +        */
> +       err = sd_read_ext_reg(card, fno, page, offset, 1, reg_buf);
> +       if (err) {
> +               pr_warn("%s: error %d reading Cache Flush bit\n",
> +                       mmc_hostname(host), err);
> +               goto out;
> +       }
> +
> +       if (reg_buf[0] & BIT(0))
> +               err = -ETIMEDOUT;
> +out:
> +       kfree(reg_buf);
> +       return err;
> +}
> +
> +static int sd_enable_cache(struct mmc_card *card)
> +{
> +       u8 *reg_buf;
> +       int err;
> +
> +       card->ext_perf.feature_enabled &= ~SD_EXT_PERF_CACHE;
> +
> +       reg_buf = kzalloc(512, GFP_KERNEL);
> +       if (!reg_buf)
> +               return -ENOMEM;
> +
> +       /*
> +        * Set Cache Enable at bit 0 in the performance enhancement register at
> +        * 260 bytes offset.
> +        */
> +       err = sd_write_ext_reg(card, card->ext_perf.fno, card->ext_perf.page,
> +                              card->ext_perf.offset + 260, BIT(0));
> +       if (err) {
> +               pr_warn("%s: error %d writing Cache Enable bit\n",
> +                       mmc_hostname(card->host), err);
> +               goto out;
> +       }
> +
> +       err = mmc_poll_for_busy(card,
> SD_WRITE_EXTR_SINGLE_TIMEOUT_MS, false,
> +                               MMC_BUSY_EXTR_SINGLE);
> +       if (!err)
> +               card->ext_perf.feature_enabled |= SD_EXT_PERF_CACHE;
> +
> +out:
> +       kfree(reg_buf);
> +       return err;
> +}
> +
>  /*
>   * Handle the detection and initialisation of a card.
>   *
> @@ -1442,6 +1533,13 @@ static int mmc_sd_init_card(struct mmc_host
> *host, u32 ocr,
>                         goto free_card;
>         }
> 
> +       /* Enable internal SD cache if supported. */
> +       if (card->ext_perf.feature_support & SD_EXT_PERF_CACHE) {
> +               err = sd_enable_cache(card);
> +               if (err)
> +                       goto free_card;
> +       }
> +
>         if (host->cqe_ops && !host->cqe_enabled) {
>                 err = host->cqe_ops->cqe_enable(host, card);
>                 if (!err) {
> @@ -1694,6 +1792,8 @@ static const struct mmc_bus_ops mmc_sd_ops = {
>         .alive = mmc_sd_alive,
>         .shutdown = mmc_sd_suspend,
>         .hw_reset = mmc_sd_hw_reset,
> +       .cache_enabled = sd_cache_enabled,
> +       .flush_cache = sd_flush_cache,
>  };
> 
>  /*
> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
> index 2867af0635f8..74e6c0624d27 100644
> --- a/include/linux/mmc/card.h
> +++ b/include/linux/mmc/card.h
> @@ -196,6 +196,7 @@ struct sd_ext_reg {
>         u8                      page;
>         u16                     offset;
>         u8                      rev;
> +       u8                      feature_enabled;
>         u8                      feature_support;
>  /* Power Management Function. */
>  #define SD_EXT_POWER_OFF_NOTIFY        (1<<0)
> --
> 2.25.1