Re: [PATCH] mmc: host: dw-mmc-rockchip: fix handling invalid clock rates

[Peter Geis]

On Thu, Mar 3, 2022 at 2:53 AM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Thu, 3 Mar 2022 at 02:52, Peter Geis <pgwipeout@xxxxxxxxx> wrote:
> >
> > The Rockchip ciu clock cannot be set as low as the dw-mmc hardware
> > supports. This leads to a situation during card initialization where the
> > ciu clock is set lower than the clock driver can support. The
> > dw-mmc-rockchip driver spews errors when this happens.
> > For normal operation this only happens a few times during boot, but when
> > cd-broken is enabled (in cases such as the SoQuartz module) this fires
> > multiple times each poll cycle.
> >
> > Fix this by testing the minimum frequency the clock driver can support
> > that is within the mmc specification, then divide that by the internal
> > clock divider. Set the f_min frequency to this value, or if it fails,
> > set f_min to the downstream driver's default.
> >
> > Fixes: f629ba2c04c9 ("mmc: dw_mmc: add support for RK3288")
> >
> > Signed-off-by: Peter Geis <pgwipeout@xxxxxxxxx>
> > ---
> >  drivers/mmc/host/dw_mmc-rockchip.c | 31 ++++++++++++++++++++++++++----
> >  1 file changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/mmc/host/dw_mmc-rockchip.c b/drivers/mmc/host/dw_mmc-rockchip.c
> > index 95d0ec0f5f3a..c198590cd74a 100644
> > --- a/drivers/mmc/host/dw_mmc-rockchip.c
> > +++ b/drivers/mmc/host/dw_mmc-rockchip.c
> > @@ -15,7 +15,9 @@
> >  #include "dw_mmc.h"
> >  #include "dw_mmc-pltfm.h"
> >
> > -#define RK3288_CLKGEN_DIV       2
> > +#define RK3288_CLKGEN_DIV      2
> > +#define RK3288_MIN_INIT_FREQ   375000
> > +#define MMC_MAX_INIT_FREQ      400000
> >
> >  struct dw_mci_rockchip_priv_data {
> >         struct clk              *drv_clk;
> > @@ -27,6 +29,7 @@ struct dw_mci_rockchip_priv_data {
> >  static void dw_mci_rk3288_set_ios(struct dw_mci *host, struct mmc_ios *ios)
> >  {
> >         struct dw_mci_rockchip_priv_data *priv = host->priv;
> > +       struct mmc_host *mmc = mmc_from_priv(host);
> >         int ret;
> >         unsigned int cclkin;
> >         u32 bus_hz;
> > @@ -34,6 +37,10 @@ static void dw_mci_rk3288_set_ios(struct dw_mci *host, struct mmc_ios *ios)
> >         if (ios->clock == 0)
> >                 return;
> >
> > +       /* the clock will fail if below the f_min rate */
> > +       if (ios->clock < mmc->f_min)
> > +               ios->clock = mmc->f_min;
> > +
>
> You shouldn't need this. The mmc core should manage this already.

I thought so too, but while setting f_min did reduce the number of
errors, it didn't stop them completely.
Each tick I was getting three failures, it turns out mmc core tries
anyways with 300000, 200000, and 100000.
Clamping it here was necessary to stop these.

>
> >         /*
> >          * cclkin: source clock of mmc controller
> >          * bus_hz: card interface clock generated by CLKGEN
> > @@ -51,7 +58,7 @@ static void dw_mci_rk3288_set_ios(struct dw_mci *host, struct mmc_ios *ios)
> >
> >         ret = clk_set_rate(host->ciu_clk, cclkin);
> >         if (ret)
> > -               dev_warn(host->dev, "failed to set rate %uHz\n", ios->clock);
> > +               dev_warn(host->dev, "failed to set rate %uHz err: %d\n", cclkin, ret);
> >
> >         bus_hz = clk_get_rate(host->ciu_clk) / RK3288_CLKGEN_DIV;
> >         if (bus_hz != host->bus_hz) {
> > @@ -290,13 +297,29 @@ static int dw_mci_rk3288_parse_dt(struct dw_mci *host)
> >
> >  static int dw_mci_rockchip_init(struct dw_mci *host)
> >  {
> > +       struct mmc_host *mmc = mmc_from_priv(host);
> > +       int ret;
> > +
> >         /* It is slot 8 on Rockchip SoCs */
> >         host->sdio_id0 = 8;
> >
> > -       if (of_device_is_compatible(host->dev->of_node,
> > -                                   "rockchip,rk3288-dw-mshc"))
> > +       if (of_device_is_compatible(host->dev->of_node, "rockchip,rk3288-dw-mshc")) {
> >                 host->bus_hz /= RK3288_CLKGEN_DIV;
> >
> > +               /* clock driver will fail if the clock is less than the lowest source clock
> > +                * divided by the internal clock divider. Test for the lowest available
> > +                * clock and set the f_min freq to clock / clock divider. If we fail, set
> > +                * it to the downstream hardcoded value.
> > +                */
> > +               ret = clk_round_rate(host->ciu_clk, MMC_MAX_INIT_FREQ * RK3288_CLKGEN_DIV);
> > +               if (ret < 0) {
> > +                       dev_warn(host->dev, "mmc safe rate failed: %d\n", ret);
> > +                       mmc->f_min = RK3288_MIN_INIT_FREQ;
> > +               } else {
> > +                       mmc->f_min = ret / RK3288_CLKGEN_DIV;
> > +               }
> > +       }
> > +
> >         return 0;
> >  }
> >
>
> Kind regards
> Uffe