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

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Date:   Thu, 3 Mar 2022 11:21:12 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Addy Ke <addy.ke@...k-chips.com>,
        Doug Anderson <dianders@...omium.org>,
        linux-mmc@...r.kernel.org,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: host: dw-mmc-rockchip: fix handling invalid clock rates

On Thu, 3 Mar 2022 at 10:49, Peter Geis <pgwipeout@...il.com> wrote:
>
> On Thu, Mar 3, 2022 at 2:53 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> >
> > On Thu, 3 Mar 2022 at 02:52, Peter Geis <pgwipeout@...il.com> 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@...il.com>
> > > ---
> > >  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.

Ohh, that was certainly a surprise to me. Unless the dw_mmc driver
invokes this path on it's own in some odd way, that means the mmc core
has a bug that we need to fix.

Would you mind taking a stack trace or debug this so we understand in
what case the mmc core doesn't respect f_min? It really should.

[...]

Kind regards
Uffe