linux-kernel - RE: [PATCH 2/2] mmc: core: Add support for cache ctrl for SD cards

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Date:   Mon, 10 May 2021 09:10:52 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] mmc: core: Add support for cache ctrl for SD cards

> +static int sd_enable_cache(struct mmc_card *card)
> +{
> +       u8 *reg_buf;
> +       int err;
> +
> +       reg_buf = kzalloc(512, GFP_KERNEL);
> +       if (!reg_buf)
> +               return -ENOMEM;
> +
> +       /*
> +        * Set the Cache Enable bit 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, 0x1);
> +       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);
I think 1sec is for flush cache, but I guess it makes sense to use it here as well.

> +       if (!err)
> +               card->ext_perf.feature_enabled |= SD_EXT_PERF_CACHE;
Maybe 
If (err)
    card->ext_perf.feature_enabled &= ~SD_EXT_PERF_CACHE;

and move to out: to catch the sd_write_ext_reg err ?

> +
> +out:
> +       kfree(reg_buf);
> +       return err;
> +}
> +
>  /*
>   * Handle the detection and initialisation of a card.
>   *
> @@ -1442,6 +1531,13 @@ 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 cache enablement failed, is it worthwhile to bail out?
Maybe disabling the cache with the appropriate message is enough?

> +       }
> +
>         if (host->cqe_ops && !host->cqe_enabled) {
>                 err = host->cqe_ops->cqe_enable(host, card);
>                 if (!err) {
> @@ -1694,6 +1790,8 @@ 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,
>  };

I would expect 2 more patches in this series:
 - flush cache on power down
 - cache disablement events?

Thanks,
Avri