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

[Ulf Hansson]

On 26 May 2014 16:21, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> 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

And one more thing, just for your information. If you intend to
support UHS cards, your need to be able to gate the clock though
->set_ios function, once the clock is 0. Let's handle that in a
separate patch - if needed though.

Kind regards
Ulf Hansson
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