Re: [PATCH v3 12/13] mmc: mmci: add explicit clk control

[Ulf Hansson]

On 23 May 2014 14:52,  <srinivas.kandagatla@xxxxxxxxxx> wrote:
> From: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
>
> On Controllers like Qcom SD card controller where cclk is mclk and mclk should
> be directly controlled by the driver.
>
> This patch adds support to control mclk directly in the driver, and also
> adds explicit_mclk_control and cclk_is_mclk flags in variant structure giving
> more flexibility to the driver.
>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
>  drivers/mmc/host/mmci.c | 30 +++++++++++++++++++++++++-----
>  1 file changed, 25 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> index 5cbf644..f6dfd24 100644
> --- a/drivers/mmc/host/mmci.c
> +++ b/drivers/mmc/host/mmci.c
> @@ -73,6 +73,8 @@ static unsigned int fmax = 515633;
>   * @pwrreg_nopower: bits in MMCIPOWER don't controls ext. power supply
>   * @mclk_delayed_writes: enable delayed writes to ensure, subsequent updates
>   *                      are not ignored.
> + * @explicit_mclk_control: enable explicit mclk control in driver.
> + * @cclk_is_mclk: enable iff card clock is multimedia card adapter clock.
>   */
>  struct variant_data {
>         unsigned int            clkreg;
> @@ -94,6 +96,8 @@ struct variant_data {
>         bool                    busy_detect;
>         bool                    pwrreg_nopower;
>         bool                    mclk_delayed_writes;
> +       bool                    explicit_mclk_control;
> +       bool                    cclk_is_mclk;

I can't see why you need to have both these new configurations. Aren't
"cclk_is_mclk" just a fact when you use "explicit_mclk_control".

I also believe I would prefer something like "qcom_clkdiv" instead.

>  };
>
>  static struct variant_data variant_arm = {
> @@ -202,6 +206,8 @@ static struct variant_data variant_qcom = {
>          * for 3 clk cycles.
>          */
>         .mclk_delayed_writes    = true,
> +       .explicit_mclk_control  = true,
> +       .cclk_is_mclk   = true,
>  };
>
>  static inline u32 mmci_readl(struct mmci_host *host, u32 off)
> @@ -317,7 +323,9 @@ static void mmci_set_clkreg(struct mmci_host *host, unsigned int desired)
>         host->cclk = 0;
>
>         if (desired) {
> -               if (desired >= host->mclk) {
> +               if (variant->cclk_is_mclk) {
> +                       host->cclk = host->mclk;
> +               } else if (desired >= host->mclk) {
>                         clk = MCI_CLK_BYPASS;
>                         if (variant->st_clkdiv)
>                                 clk |= MCI_ST_UX500_NEG_EDGE;
> @@ -1354,6 +1362,16 @@ static void mmci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
>         if (!ios->clock && variant->pwrreg_clkgate)
>                 pwr &= ~MCI_PWR_ON;
>
> +       if (ios->clock != host->mclk && host->variant->explicit_mclk_control) {

I suggest you should clarify the statement by adding a pair of extra
parentheses. Additionally it seems like a good idea to reverse the
order of the statements, to clarify this is for qcom clock handling
only.

More important, what I think you really want to do is to compare
"ios->clock" with it's previous value it had when ->set_ios were
invoked. Then let a changed value act as the trigger to set a new clk
rate. Obvoiusly you need to cache the clock rate in the struct mmci
host to handle this.

> +               int rc = clk_set_rate(host->clk, ios->clock);
> +               if (rc < 0) {
> +                       dev_err(mmc_dev(host->mmc),
> +                               "Error setting clock rate (%d)\n", rc);
> +               } else {
> +                       host->mclk = clk_get_rate(host->clk);

So here you actually find out the new clk rate, but shouldn't you
update "host->mclk" within the spin_lock? Or it might not matter?

> +               }
> +       }
> +
>         spin_lock_irqsave(&host->lock, flags);
>
>         mmci_set_clkreg(host, ios->clock);
> @@ -1540,10 +1558,12 @@ static int mmci_probe(struct amba_device *dev,
>          * is not specified. Either value must not exceed the clock rate into
>          * the block, of course.
>          */
> -       if (mmc->f_max)
> -               mmc->f_max = min(host->mclk, mmc->f_max);
> -       else
> -               mmc->f_max = min(host->mclk, fmax);
> +       if (!host->variant->explicit_mclk_control) {
> +               if (mmc->f_max)
> +                       mmc->f_max = min(host->mclk, mmc->f_max);
> +               else
> +                       mmc->f_max = min(host->mclk, fmax);
> +       }

This means your mmc->f_max value will either be zero or the one you
provided through DT. And since zero won't work, that means you
_require_ to get the value from DT. According to the documentation of
this DT binding, f_max is optional.

So unless you fine another way of dynamically at runtime figure out
the value of f_max (using the clk API), you need to update the DT
documentation for mmci.

Additionally, this makes me wonder about f_min. I haven't seen
anywhere in this patch were that value is being set to proper value,
right?

>         dev_dbg(mmc_dev(mmc), "clocking block at %u Hz\n", mmc->f_max);
>
>         /* Get regulators and the supported OCR mask */
> --
> 1.9.1
>

Kind regards
Ulf Hansson
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