Date:   Thu, 8 Dec 2022 21:00:50 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     <linux-clk@...r.kernel.org>, Stephen Boyd <sboyd@...nel.org>,
        <linux-arm-msm@...r.kernel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Douglas Anderson <dianders@...omium.org>,
        <dri-devel@...ts.freedesktop.org>,
        Stephen Boyd <swboyd@...omium.org>,
        <krzysztof.kozlowski@...aro.org>, Rob Clark <robdclark@...il.com>,
        Andy Gross <agross@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Michael Turquette <mturquette@...libre.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [Freedreno] [PATCH v7 3/6] clk: qcom: gdsc: Add a reset op to
 poll gdsc collapse

On 12/8/2022 8:32 PM, Akhil P Oommen wrote:
> On 12/7/2022 9:15 PM, Ulf Hansson wrote:
>> On Wed, 5 Oct 2022 at 11:08, Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>>> Add a reset op compatible function to poll for gdsc collapse. This is
>>> required because:
>>>   1. We don't wait for it to turn OFF at hardware for VOTABLE GDSCs.
>>>   2. There is no way for client drivers (eg. gpu driver) to do
>>>   put-with-wait for these gdscs which is required in some scenarios
>>>   (eg. GPU recovery).
>> What puzzles me a bit, who is the typical consumer of the reset.
>>
>> I looked at patch4 and tried to figure it out, but let's discuss that
>> in that thread instead. Some more comments, see below.
> https://patchwork.freedesktop.org/patch/498397/
> gpu driver side changes are already merged in upstream. We call this interface during a GPU recovery which is supposed to be a rare event.
>>> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>> ---
>>>
>>> Changes in v7:
>>> - Update commit message (Bjorn)
>>>
>>> Changes in v2:
>>> - Minor update to function prototype
>>>
>>>  drivers/clk/qcom/gdsc.c | 23 +++++++++++++++++++----
>>>  drivers/clk/qcom/gdsc.h |  7 +++++++
>>>  2 files changed, 26 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
>>> index 7cf5e13..ccef742 100644
>>> --- a/drivers/clk/qcom/gdsc.c
>>> +++ b/drivers/clk/qcom/gdsc.c
>>> @@ -17,6 +17,7 @@
>>>  #include <linux/reset-controller.h>
>>>  #include <linux/slab.h>
>>>  #include "gdsc.h"
>>> +#include "reset.h"
>>>
>>>  #define PWR_ON_MASK            BIT(31)
>>>  #define EN_REST_WAIT_MASK      GENMASK_ULL(23, 20)
>>> @@ -116,7 +117,8 @@ static int gdsc_hwctrl(struct gdsc *sc, bool en)
>>>         return regmap_update_bits(sc->regmap, sc->gdscr, HW_CONTROL_MASK, val);
>>>  }
>>>
>>> -static int gdsc_poll_status(struct gdsc *sc, enum gdsc_status status)
>>> +static int gdsc_poll_status(struct gdsc *sc, enum gdsc_status status,
>>> +               s64 timeout_us, unsigned int interval_ms)
>>>  {
>>>         ktime_t start;
>>>
>>> @@ -124,7 +126,9 @@ static int gdsc_poll_status(struct gdsc *sc, enum gdsc_status status)
>>>         do {
>>>                 if (gdsc_check_status(sc, status))
>>>                         return 0;
>>> -       } while (ktime_us_delta(ktime_get(), start) < TIMEOUT_US);
>>> +               if (interval_ms)
>>> +                       msleep(interval_ms);
>>> +       } while (ktime_us_delta(ktime_get(), start) < timeout_us);
>> Rather than continue to open code this polling loop, would it not make
>> sense to convert the code into using readx_poll_timeout() (or some of
>> its friends).
> I was going for a minimal code churn to get this mainlined easily. I like the idea, perhaps we can have a refactor patch if there is consensus.
>
> -Akhil.
>> Down the road, this leads to that the msleep() above should become
>> usleep_range() instead, which seems more correct to me.
Btw, we can optimize this a bit more using 'completion' to minimize CPU overhead. But that can wait as this is supposed to be a rarely used path. We don't expect gpu faults often. I would like to see a simpler implementation upstream first.

-Akhil.
>>
>>>         if (gdsc_check_status(sc, status))
>>>                 return 0;
>>> @@ -189,7 +193,7 @@ static int gdsc_toggle_logic(struct gdsc *sc, enum gdsc_status status)
>>>                 udelay(1);
>>>         }
>>>
>>> -       ret = gdsc_poll_status(sc, status);
>>> +       ret = gdsc_poll_status(sc, status, TIMEOUT_US, 0);
>>>         WARN(ret, "%s status stuck at 'o%s'", sc->pd.name, status ? "ff" : "n");
>>>
>>>         if (!ret && status == GDSC_OFF && sc->rsupply) {
>>> @@ -360,7 +364,7 @@ static int _gdsc_disable(struct gdsc *sc)
>>>                  */
>>>                 udelay(1);
>>>
>>> -               ret = gdsc_poll_status(sc, GDSC_ON);
>>> +               ret = gdsc_poll_status(sc, GDSC_ON, TIMEOUT_US, 0);
>>>                 if (ret)
>>>                         return ret;
>>>         }
>>> @@ -608,3 +612,14 @@ int gdsc_gx_do_nothing_enable(struct generic_pm_domain *domain)
>>>         return 0;
>>>  }
>>>  EXPORT_SYMBOL_GPL(gdsc_gx_do_nothing_enable);
>>> +
>>> +int gdsc_wait_for_collapse(void *priv)
>>> +{
>>> +       struct gdsc *sc = priv;
>>> +       int ret;
>>> +
>>> +       ret = gdsc_poll_status(sc, GDSC_OFF, 500000, 5);
>>> +       WARN(ret, "%s status stuck at 'on'", sc->pd.name);
>>> +       return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(gdsc_wait_for_collapse);
>>> diff --git a/drivers/clk/qcom/gdsc.h b/drivers/clk/qcom/gdsc.h
>>> index 981a12c..5395f69 100644
>>> --- a/drivers/clk/qcom/gdsc.h
>>> +++ b/drivers/clk/qcom/gdsc.h
>>> @@ -12,6 +12,7 @@
>>>  struct regmap;
>>>  struct regulator;
>>>  struct reset_controller_dev;
>>> +struct qcom_reset_map;
>>>
>>>  /**
>>>   * struct gdsc - Globally Distributed Switch Controller
>>> @@ -88,6 +89,7 @@ int gdsc_register(struct gdsc_desc *desc, struct reset_controller_dev *,
>>>                   struct regmap *);
>>>  void gdsc_unregister(struct gdsc_desc *desc);
>>>  int gdsc_gx_do_nothing_enable(struct generic_pm_domain *domain);
>>> +int gdsc_wait_for_collapse(void *priv);
>>>  #else
>>>  static inline int gdsc_register(struct gdsc_desc *desc,
>>>                                 struct reset_controller_dev *rcdev,
>>> @@ -97,5 +99,10 @@ static inline int gdsc_register(struct gdsc_desc *desc,
>>>  }
>>>
>>>  static inline void gdsc_unregister(struct gdsc_desc *desc) {};
>>> +
>>> +static int gdsc_wait_for_collapse(void *priv)
>>> +{
>>> +       return  -ENOSYS;
>>> +}
>>>  #endif /* CONFIG_QCOM_GDSC */
>>>  #endif /* __QCOM_GDSC_H__ */
>> Kind regards
>> Uffe

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