Re: [PATCH v2] mmc: sdhci-msm: Boost controller core clock

[Stephen Boyd]

On 11/09, Ulf Hansson wrote:
> On 7 November 2015 at 00:39, Bjorn Andersson
> <bjorn.andersson@xxxxxxxxxxxxxx> wrote:
> > On Fri 06 Nov 00:10 PST 2015, Ulf Hansson wrote:
> >
> >> On 6 November 2015 at 02:42, Bjorn Andersson <bjorn@xxxxxxx> wrote:
> >> > On Mon, Jul 6, 2015 at 4:53 AM, Ivan T. Ivanov <ivan.ivanov@xxxxxxxxxx> wrote:
> >> >> Ensure SDCC is working with maximum clock otherwise card
> >> >> detection could be extremely slow, up to 7 seconds.
> >> >>
> >> >> Signed-off-by: Ivan T. Ivanov <ivan.ivanov@xxxxxxxxxx>
> >> >> Reviewed-by: Georgi Djakov <georgi.djakov@xxxxxxxxxx>
> >> >> Acked-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> >> >> ---
> >> >>
> >> >> Changes since v0:
> >> >> - s/falied/failed in warning message.
> >> >>
> >> >>  drivers/mmc/host/sdhci-msm.c | 5 +++++
> >> >>  1 file changed, 5 insertions(+)
> >> >>
> >> >> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> >> >> index 4a09f76..4bcee03 100644
> >> >> --- a/drivers/mmc/host/sdhci-msm.c
> >> >> +++ b/drivers/mmc/host/sdhci-msm.c
> >> >> @@ -489,6 +489,11 @@ static int sdhci_msm_probe(struct platform_device *pdev)
> >> >>                 goto pclk_disable;
> >> >>         }
> >> >>
> >> >> +       /* Vote for maximum clock rate for maximum performance */
> >> >> +       ret = clk_set_rate(msm_host->clk, INT_MAX);
> >> >> +       if (ret)
> >> >> +               dev_warn(&pdev->dev, "core clock boost failed\n");
> >> >> +
> >> >
> >> > On my 8974AC devices this results in GCC_SDCC1_APPS_CLK changing from
> >> > 100MHz to 200MHz for my eMMC. Unfortunately this results in the
> >> > following error:
> >> >
> >> > [    5.103241] mmcblk0: retrying because a re-tune was needed
> >> > [    5.109270] mmcblk0: error -84 transferring data, sector 5816322,
> >> > nr 2, cmd response 0x900, card status 0xc00
> >> >
> >> > Looking at the board specification it's stated that these card should
> >> > run in DDR50, so I've tried specifying "max-frequency" in the dt. I
> >> > verified in sdhci_set_clock() that we get a divisor of 4, but the
> >> > result is a repetition of:
> >>
> >> I don't follow. Are you saying that changing the clock frequency to
> >> 200MHz caused the card to be initialized in HS200 mode instead of
> >> DDR50?
> >>
> >
> > No, we clock the sdhci block at 100MHz, the host->max_clk is 200MHz and
> > the divisor in sdhci_set_clock() becomes 1. So if I read this correctly
> > we're running HS200 at 100MHz.
> >
> > Bumping the clock rate to 200MHz at the block doesn't affect the max_clk
> > and hence we're trying to run the bus at 200MHz.
> >
> > I therefor tried to just set "max-frequency" to 50MHz, getting the
> > divider to be 4 and the below error.
> >
> > So I assume it just happened to work at 100MHz, but 200MHz is way off
> > from the 50MHz the board is designed and tested for.
> >
> >
> > Unfortunately I don't have the equipment to measure these assumptions :/
> 
> Ahh, I see.
> 
> It seems like a reasonable assumption that the controller can't cope
> with a higher clock rate than 100 MHz as "input" clock. That would
> then mean that there are different versions of the controller, as it
> seems like for some version it's fine with 200MHz and for some 100MHz.
> 
> According to the DT compatible strings, *one* version is currently
> supported, "qcom,sdhci-msm-v4"...

The same version of hardware is there 4 times. The difference is
the maximum clock frequency supported by them is different. In
downstream kernels we've handled this by trimming the frequency
tables for the different controllers in the clock driver.
Setting the clock to INT_MAX will make it run at 400MHz, which
doesn't look to be supported by anything besides sdc1 on 8974ac.

> 
> I see two viable solutions. One would be to limit the clock rate
> depending on the version of the controller (new compatible strings
> needs to be added). Another one would be to limit the clock rate by
> using the existing DT binding for max-frequency, and thus do a
> clk_set_rate(mmc->f_max) during probe.
> 

I'd rather see that done via OPP tables in DT, but I suppose
max-frequency is fine too. We'll need to use OPPs soon enough
because there's a voltage associated with that frequency.

In case you're wondering, the max frequency for sdc1 on 8974ac is
400MHz. If it's just a plain 8974pro then the max frequency is
200MHz. Otherwise, sdc2 maxes out at 200Mhz and sdc3 and sdc4 max
out at 100MHz.

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