Date:   Thu, 15 Dec 2022 09:12:23 -0800
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>
CC:     <robdclark@...il.com>, <sean@...rly.run>, <vkoul@...nel.org>,
        <daniel@...ll.ch>, <airlied@...il.com>, <agross@...nel.org>,
        <dmitry.baryshkov@...aro.org>, <andersson@...nel.org>,
        <quic_sbillaka@...cinc.com>, <freedreno@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/dp: do not complete dp_aux_cmd_fifo_tx() if irq
 is not for aux transfer


On 12/14/2022 6:59 PM, Abhinav Kumar wrote:
> Hi Stephen
>
> On 12/14/2022 4:29 PM, Stephen Boyd wrote:
>> Quoting Doug Anderson (2022-12-14 16:14:42)
>>> Hi,
>>>
>>> On Wed, Dec 14, 2022 at 3:46 PM Abhinav Kumar 
>>> <quic_abhinavk@...cinc.com> wrote:
>>>>
>>>> Hi Doug
>>>>
>>>> On 12/14/2022 2:29 PM, Doug Anderson wrote:
>>>>> Hi,
>>>>>
>>>>> On Wed, Dec 14, 2022 at 1:21 PM Kuogee Hsieh 
>>>>> <quic_khsieh@...cinc.com> wrote:
>>>>>>
>>>>>> There are 3 possible interrupt sources are handled by DP controller,
>>>>>> HPDstatus, Controller state changes and Aux read/write transaction.
>>>>>> At every irq, DP controller have to check isr status of every 
>>>>>> interrupt
>>>>>> sources and service the interrupt if its isr status bits shows 
>>>>>> interrupts
>>>>>> are pending. There is potential race condition may happen at 
>>>>>> current aux
>>>>>> isr handler implementation since it is always complete 
>>>>>> dp_aux_cmd_fifo_tx()
>>>>>> even irq is not for aux read or write transaction. This may cause 
>>>>>> aux read
>>>>>> transaction return premature if host aux data read is in the 
>>>>>> middle of
>>>>>> waiting for sink to complete transferring data to host while irq 
>>>>>> happen.
>>>>>> This will cause host's receiving buffer contains unexpected data. 
>>>>>> This
>>>>>> patch fixes this problem by checking aux isr and return 
>>>>>> immediately at
>>>>>> aux isr handler if there are no any isr status bits set.
>>>>>>
>>>>>> Follows are the signature at kernel logs when problem happen,
>>>>>> EDID has corrupt header
>>>>>> panel-simple-dp-aux aux-aea0000.edp: Couldn't identify panel via 
>>>>>> EDID
>>>>>> panel-simple-dp-aux aux-aea0000.edp: error -EIO: Couldn't detect 
>>>>>> panel nor find a fallback
>>>>>>
>>>>>> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>>>>>> ---
>>>>>>    drivers/gpu/drm/msm/dp/dp_aux.c | 7 +++++++
>>>>>>    1 file changed, 7 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c 
>>>>>> b/drivers/gpu/drm/msm/dp/dp_aux.c
>>>>>> index d030a93..8f8b12a 100644
>>>>>> --- a/drivers/gpu/drm/msm/dp/dp_aux.c
>>>>>> +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
>>>>>> @@ -423,6 +423,13 @@ void dp_aux_isr(struct drm_dp_aux *dp_aux)
>>>>>>
>>>>>>           isr = dp_catalog_aux_get_irq(aux->catalog);
>>>>>>
>>>>>> +       /*
>>>>>> +        * if this irq is not for aux transfer,
>>>>>> +        * then return immediately
>>>>>> +        */
>>>>>
>>>>> Why do you need 4 lines for a comment that fits on one line?
>>>> Yes, we can fit this to one line.
>>>>>
>>>>>> +       if (!isr)
>>>>>> +               return;
>>>>>
>>>>> I can confirm that this works for me. I could reproduce the EDID
>>>>> problems in the past and I can't after this patch. ...so I could give
>>>>> a:
>>>>>
>>>>> Tested-by: Douglas Anderson <dianders@...omium.org>
>>>>>
>>>>> I'm not an expert on this part of the code, so feel free to ignore my
>>>>> other comments if everyone else thinks this patch is fine as-is, but
>>>>> to me something here feels a little fragile. It feels a little weird
>>>>> that we'll "complete" for _any_ interrupt that comes through now
>>>>> rather than relying on dp_aux_native_handler() / dp_aux_i2c_handler()
>>>>> to specifically identify interrupts that caused the end of the
>>>>> transfer. I guess that idea is that every possible interrupt we get
>>>>> causes the end of the transfer?
>>>>>
>>>>> -Doug
>>>>
>>>> So this turned out to be more tricky and was a good finding from 
>>>> kuogee.
>>>>
>>>> In the bad EDID case, it was technically not bad EDID.
>>>>
>>>> What was happening was, the VIDEO_READY interrupt was continuously
>>>> firing. Ideally, this should fire only once but due to some error
>>>> condition it kept firing. We dont exactly know why yet what was the
>>>> error condition making it continuously fire.
>>
>> This is a great detail that is missing from the commit text.
>>
> Yup, we should update this.
>>>>
>>>> In the DP ISR, the dp_aux_isr() gets called even if it was not an aux
>>>> interrupt which fired (so the call flow in this case was
>>>> dp_display_irq_handler (triggered for VIDEO_READY) ---> dp_aux_isr()
>>>> So we should certainly have some protection to return early from this
>>>> routine if there was no aux interrupt which fired.
>>
>> I'm not sure that's a race condition though, more like a problem where
>> the completion is called unconditionally?
>>
>
> hmm ... True.
>
>>>>
>>>> Which is what this fix is doing.
>>>>
>>>> Its not completing any interrupt, its just returning early if no aux
>>>> interrupt fired.
>>>
>>> ...but the whole problem was that it was doing the complete() at the
>>> end, right? Kuogee even mentioned that in the commit message.
>>> Specifically, I checked dp_aux_native_handler() and
>>> dp_aux_i2c_handler(), both of which are passed the "isr". Unless I
>>> messed up, both functions already were no-ops if the ISR was 0, even
>>> before Kuogee's patch. That means that the only thing Kuogee's patch
>>> does is to prevent the call to "complete(&aux->comp)" at the end of
>>> "dp_aux_isr()".
>>>
>>> ...and it makes sense not to call the complete() if no "isr" is 0.
>>> ...but what I'm saying is that _any_ non-zero value of ISR will still
>>> cause the complete() to be called after Kuogee's patch. That means
>>> that if any of the 32-bits in the "isr" variable are set, that we will
>>> call complete(). I'm asking if you're sure that every single bit of
>>> the "isr" means that we're ready to call complete(). It feels like it
>>> would be less fragile if dp_aux_native_handler() and
>>> dp_aux_i2c_handler() (which both already look at the ISR) returned
>>> some value saying whether the "isr" contained a bit that meant that
>>> complete() should be called.
>>>
>>
>> I'm almost certain I've asked for this before, but I can't find it
>> anymore. Can we also simplify the aux handlers to be a big pile of
>> if-else-if conditions that don't overwrite the 'aux_error_num'? That
>> would simplify the patch below.
>>
>
> Okay, this makes it much clear about what Doug was trying to explain.
>
> This certainly improves the irq return code better (handled Vs none).
>
> In terms of the functionality of it, although it looks too simple, the 
> current change was okay.
>
> But, I agree that this would be more robust in terms of the irq return 
> codes.
>
> Kuogee, any concerns with this?
no, let me improve the aux is handler.
>
>> ---8<---
>> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c 
>> b/drivers/gpu/drm/msm/dp/dp_aux.c
>> index d030a93a08c3..ff79cad90d21 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_aux.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
>> @@ -162,45 +162,73 @@ static ssize_t dp_aux_cmd_fifo_rx(struct
>> dp_aux_private *aux,
>>       return i;
>>   }
>>
>> -static void dp_aux_native_handler(struct dp_aux_private *aux, u32 isr)
>> +static irqreturn_t dp_aux_native_handler(struct dp_aux_private *aux, 
>> u32 isr)
>>   {
>> -    if (isr & DP_INTR_AUX_I2C_DONE)
>> +    irqreturn_t ret = IRQ_NONE;
>> +
>> +    if (isr & DP_INTR_AUX_I2C_DONE) {
>>           aux->aux_error_num = DP_AUX_ERR_NONE;
>> -    else if (isr & DP_INTR_WRONG_ADDR)
>> +        ret = IRQ_HANDLED;
>> +    } else if (isr & DP_INTR_WRONG_ADDR) {
>>           aux->aux_error_num = DP_AUX_ERR_ADDR;
>> -    else if (isr & DP_INTR_TIMEOUT)
>> +        ret = IRQ_HANDLED;
>> +    } else if (isr & DP_INTR_TIMEOUT) {
>>           aux->aux_error_num = DP_AUX_ERR_TOUT;
>> -    if (isr & DP_INTR_NACK_DEFER)
>> +        ret = IRQ_HANDLED;
>> +    }
>> +
>> +    if (isr & DP_INTR_NACK_DEFER) {
>>           aux->aux_error_num = DP_AUX_ERR_NACK;
>> +        ret = IRQ_HANDLED;
>> +    }
>>       if (isr & DP_INTR_AUX_ERROR) {
>>           aux->aux_error_num = DP_AUX_ERR_PHY;
>>           dp_catalog_aux_clear_hw_interrupts(aux->catalog);
>> +        ret = IRQ_HANDLED;
>>       }
>> +
>> +    return ret;
>>   }
>>
>> -static void dp_aux_i2c_handler(struct dp_aux_private *aux, u32 isr)
>> +static irqreturn_t dp_aux_i2c_handler(struct dp_aux_private *aux, 
>> u32 isr)
>>   {
>> +    irqreturn_t ret = IRQ_NONE;
>> +
>>       if (isr & DP_INTR_AUX_I2C_DONE) {
>>           if (isr & (DP_INTR_I2C_NACK | DP_INTR_I2C_DEFER))
>>               aux->aux_error_num = DP_AUX_ERR_NACK;
>>           else
>>               aux->aux_error_num = DP_AUX_ERR_NONE;
>> -    } else {
>> -        if (isr & DP_INTR_WRONG_ADDR)
>> -            aux->aux_error_num = DP_AUX_ERR_ADDR;
>> -        else if (isr & DP_INTR_TIMEOUT)
>> -            aux->aux_error_num = DP_AUX_ERR_TOUT;
>> -        if (isr & DP_INTR_NACK_DEFER)
>> -            aux->aux_error_num = DP_AUX_ERR_NACK_DEFER;
>> -        if (isr & DP_INTR_I2C_NACK)
>> -            aux->aux_error_num = DP_AUX_ERR_NACK;
>> -        if (isr & DP_INTR_I2C_DEFER)
>> -            aux->aux_error_num = DP_AUX_ERR_DEFER;
>> -        if (isr & DP_INTR_AUX_ERROR) {
>> -            aux->aux_error_num = DP_AUX_ERR_PHY;
>> - dp_catalog_aux_clear_hw_interrupts(aux->catalog);
>> -        }
>> +        return IRQ_HANDLED;
>> +    }
>> +
>> +    if (isr & DP_INTR_WRONG_ADDR) {
>> +        aux->aux_error_num = DP_AUX_ERR_ADDR;
>> +        ret = IRQ_HANDLED;
>> +    } else if (isr & DP_INTR_TIMEOUT) {
>> +        aux->aux_error_num = DP_AUX_ERR_TOUT;
>> +        ret = IRQ_HANDLED;
>> +    }
>> +
>> +    if (isr & DP_INTR_NACK_DEFER) {
>> +        aux->aux_error_num = DP_AUX_ERR_NACK_DEFER;
>> +        ret = IRQ_HANDLED;
>> +    }
>> +    if (isr & DP_INTR_I2C_NACK) {
>> +        aux->aux_error_num = DP_AUX_ERR_NACK;
>> +        ret = IRQ_HANDLED;
>> +    }
>> +    if (isr & DP_INTR_I2C_DEFER) {
>> +        aux->aux_error_num = DP_AUX_ERR_DEFER;
>> +        ret = IRQ_HANDLED;
>> +    }
>> +    if (isr & DP_INTR_AUX_ERROR) {
>> +        aux->aux_error_num = DP_AUX_ERR_PHY;
>> +        dp_catalog_aux_clear_hw_interrupts(aux->catalog);
>> +        ret = IRQ_HANDLED;
>>       }
>> +
>> +    return ret;
>>   }
>>
>>   static void dp_aux_update_offset_and_segment(struct dp_aux_private 
>> *aux,
>> @@ -409,14 +437,15 @@ static ssize_t dp_aux_transfer(struct 
>> drm_dp_aux *dp_aux,
>>       return ret;
>>   }
>>
>> -void dp_aux_isr(struct drm_dp_aux *dp_aux)
>> +irqreturn_t dp_aux_isr(struct drm_dp_aux *dp_aux)
>>   {
>>       u32 isr;
>>       struct dp_aux_private *aux;
>> +    irqreturn_t ret = IRQ_NONE;
>>
>>       if (!dp_aux) {
>>           DRM_ERROR("invalid input\n");
>> -        return;
>> +        return ret;
>>       }
>>
>>       aux = container_of(dp_aux, struct dp_aux_private, dp_aux);
>> @@ -424,14 +453,17 @@ void dp_aux_isr(struct drm_dp_aux *dp_aux)
>>       isr = dp_catalog_aux_get_irq(aux->catalog);
>>
>>       if (!aux->cmd_busy)
>> -        return;
>> +        return ret;
>>
>>       if (aux->native)
>> -        dp_aux_native_handler(aux, isr);
>> +        ret |= dp_aux_native_handler(aux, isr);
>>       else
>> -        dp_aux_i2c_handler(aux, isr);
>> +        ret |= dp_aux_i2c_handler(aux, isr);
>>
>> -    complete(&aux->comp);
>> +    if (ret == IRQ_HANDLED)
>> +        complete(&aux->comp);
>> +
>> +    return ret;
>>   }
>>
>>   void dp_aux_reconfig(struct drm_dp_aux *dp_aux)
>> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.h 
>> b/drivers/gpu/drm/msm/dp/dp_aux.h
>> index e930974bcb5b..511305da4f66 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_aux.h
>> +++ b/drivers/gpu/drm/msm/dp/dp_aux.h
>> @@ -11,7 +11,7 @@
>>
>>   int dp_aux_register(struct drm_dp_aux *dp_aux);
>>   void dp_aux_unregister(struct drm_dp_aux *dp_aux);
>> -void dp_aux_isr(struct drm_dp_aux *dp_aux);
>> +irqreturn_t dp_aux_isr(struct drm_dp_aux *dp_aux);
>>   void dp_aux_init(struct drm_dp_aux *dp_aux);
>>   void dp_aux_deinit(struct drm_dp_aux *dp_aux);
>>   void dp_aux_reconfig(struct drm_dp_aux *dp_aux);
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c 
>> b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index dd26ca651a05..10c6d6847163 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> @@ -1979,13 +1979,11 @@ int dp_ctrl_off(struct dp_ctrl *dp_ctrl)
>>       return ret;
>>   }
>>
>> -void dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
>> +irqreturn_t dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
>>   {
>>       struct dp_ctrl_private *ctrl;
>>       u32 isr;
>> -
>> -    if (!dp_ctrl)
>> -        return;
>> +    irqreturn_t ret = IRQ_NONE;
>>
>>       ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
>>
>> @@ -1994,12 +1992,16 @@ void dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
>>       if (isr & DP_CTRL_INTR_READY_FOR_VIDEO) {
>>           drm_dbg_dp(ctrl->drm_dev, "dp_video_ready\n");
>>           complete(&ctrl->video_comp);
>> +        ret = IRQ_HANDLED;
>>       }
>>
>>       if (isr & DP_CTRL_INTR_IDLE_PATTERN_SENT) {
>>           drm_dbg_dp(ctrl->drm_dev, "idle_patterns_sent\n");
>>           complete(&ctrl->idle_comp);
>> +        ret = IRQ_HANDLED;
>>       }
>> +
>> +    return ret;
>>   }
>>
>>   struct dp_ctrl *dp_ctrl_get(struct device *dev, struct dp_link *link,
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h 
>> b/drivers/gpu/drm/msm/dp/dp_ctrl.h
>> index 9f29734af81c..c3af06dc87b1 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
>> @@ -25,7 +25,7 @@ int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
>>   int dp_ctrl_off_link(struct dp_ctrl *dp_ctrl);
>>   int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
>>   void dp_ctrl_push_idle(struct dp_ctrl *dp_ctrl);
>> -void dp_ctrl_isr(struct dp_ctrl *dp_ctrl);
>> +irqreturn_t dp_ctrl_isr(struct dp_ctrl *dp_ctrl);
>>   void dp_ctrl_handle_sink_request(struct dp_ctrl *dp_ctrl);
>>   struct dp_ctrl *dp_ctrl_get(struct device *dev, struct dp_link *link,
>>               struct dp_panel *panel,    struct drm_dp_aux *aux,
>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c
>> b/drivers/gpu/drm/msm/dp/dp_display.c
>> index a49f6dbbe888..559d9ab7954d 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>> @@ -1192,7 +1192,7 @@ static int dp_hpd_event_thread_start(struct
>> dp_display_private *dp_priv)
>>   static irqreturn_t dp_display_irq_handler(int irq, void *dev_id)
>>   {
>>       struct dp_display_private *dp = dev_id;
>> -    irqreturn_t ret = IRQ_HANDLED;
>> +    irqreturn_t ret = IRQ_NONE;
>>       u32 hpd_isr_status;
>>
>>       if (!dp) {
>> @@ -1206,27 +1206,33 @@ static irqreturn_t dp_display_irq_handler(int
>> irq, void *dev_id)
>>           drm_dbg_dp(dp->drm_dev, "type=%d isr=0x%x\n",
>>               dp->dp_display.connector_type, hpd_isr_status);
>>           /* hpd related interrupts */
>> -        if (hpd_isr_status & DP_DP_HPD_PLUG_INT_MASK)
>> +        if (hpd_isr_status & DP_DP_HPD_PLUG_INT_MASK) {
>>               dp_add_event(dp, EV_HPD_PLUG_INT, 0, 0);
>> +            ret = IRQ_HANDLED;
>> +        }
>>
>>           if (hpd_isr_status & DP_DP_IRQ_HPD_INT_MASK) {
>>               dp_add_event(dp, EV_IRQ_HPD_INT, 0, 0);
>> +            ret = IRQ_HANDLED;
>>           }
>>
>>           if (hpd_isr_status & DP_DP_HPD_REPLUG_INT_MASK) {
>>               dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 0);
>>               dp_add_event(dp, EV_HPD_PLUG_INT, 0, 3);
>> +            ret = IRQ_HANDLED;
>>           }
>>
>> -        if (hpd_isr_status & DP_DP_HPD_UNPLUG_INT_MASK)
>> +        if (hpd_isr_status & DP_DP_HPD_UNPLUG_INT_MASK) {
>>               dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 0);
>> +            ret = IRQ_HANDLED;
>> +        }
>>       }
>>
>>       /* DP controller isr */
>> -    dp_ctrl_isr(dp->ctrl);
>> +    ret |= dp_ctrl_isr(dp->ctrl);
>>
>>       /* DP aux isr */
>> -    dp_aux_isr(dp->aux);
>> +    ret |= dp_aux_isr(dp->aux);
>>
>>       return ret;
>>   }

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