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SubjectRe: [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@codeaurora.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@chromium.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.

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