linux-kernel - Re: [RFT PATCH v2 06/10] drivers: qcom: rpmh-rsc: Comment tcs_is

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Date:   Thu, 2 Apr 2020 13:19:11 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Maulik Shah <mkshah@...eaurora.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Evan Green <evgreen@...omium.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v2 06/10] drivers: qcom: rpmh-rsc: Comment
 tcs_is_free() + warn if state mismatch

Hi,

On Wed, Apr 1, 2020 at 4:39 AM Maulik Shah <mkshah@...eaurora.org> wrote:
>
> Hi,
>
> On 3/12/2020 4:43 AM, Douglas Anderson wrote:
> > tcs_is_free() had two checks in it: does the software think that the
> > TCS is free and does the hardware think that the TCS is free.  Let's
> > comment this and also add a warning in the case that software and
> > hardware disagree, at least for ACTIVE_ONLY TCS.
> >
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> >
> > Changes in v2:
> > - Comment tcs_is_free() new for v2; replaces old patch 6.
> >
> >   drivers/soc/qcom/rpmh-rsc.c | 23 +++++++++++++++++++++--
> >   1 file changed, 21 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> > index 9d2669cbd994..93f5d1fb71ca 100644
> > --- a/drivers/soc/qcom/rpmh-rsc.c
> > +++ b/drivers/soc/qcom/rpmh-rsc.c
> > @@ -181,8 +181,27 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,
> >    */
> >   static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
> >   {
> > -     return !test_bit(tcs_id, drv->tcs_in_use) &&
> > -            read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id);
> > +     /* If software thinks it's in use then it's definitely in use */
> > +     if (test_bit(tcs_id, drv->tcs_in_use))
> > +             return false;
> > +
> > +     /* If hardware agrees it's free then it's definitely free */
> > +     if (read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id) != 0)
> > +             return true;
> > +
> > +     /*
> > +      * If we're here then software and hardware disagree about whether
> > +      * the TCS is free.  Software thinks it is free and hardware thinks
> > +      * it is not.
> > +      *
> > +      * Maybe this should be a warning in all cases, but it's almost
> > +      * certainly a warning for the ACTIVE_TCS where nobody else should
> > +      * be doing anything else behind our backs.  For now we'll just
> > +      * warn there and then still return that we're in use.
> > +      */
> > +     WARN(drv->tcs[tcs_id].type == ACTIVE_TCS,
> > +          "Driver thought TCS was free but HW reported busy\n");
> This warning can come for borrowed WAKE_TCS as well.
> > +     return false;
> >   }
>
> We have a patch on downstream variant to optimize this by only checking
> tcs_in_use flag (SW check) and HW check is removed.
>
>   static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
>   {
> -       return !test_bit(tcs_id, drv->tcs_in_use) &&
> -              read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id, 0);
> +       return !test_bit(tcs_id, drv->tcs_in_use);
>   }
>
> With this we are good and don't require to put above warning as well.
>
> if you want me to upload, i can post it and then you can drop this
> change from your series.
>
> Or if you want to modify it as above and keep in this series i am ok.

Probably easiest for me to replace this patch in the series with one
that removes the read from RSC_DRV_STATUS.  Then it will all be
clearer.