[Freedreno] [PATCH v2 2/2] drm/msm/dsi: implement opp table based check for dsi_mgr_bridge_mode_valid()

[Abhinav Kumar]

On 1/11/2023 2:56 PM, Dmitry Baryshkov wrote:
> On 12/01/2023 00:52, Abhinav Kumar wrote:
>> Currently there is no protection against a user trying to set
>> an unsupported mode on DSI. Implement a check based on the opp
>> table whether the byte clock for the mode can be supported by
>> validating whether an opp table entry exists.
>>
>> For devices which have not added opp table support yet, skip
>> this check otherwise it will break bootup on those devices.
>>
>> changes in v2:
>>     - drop dev_pm_opp_get_opp_table() usage
>>
>> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/15
>> Reported-by: Rob Clark <robdclark at gmail.com>
>> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
>> ---
>>   drivers/gpu/drm/msm/dsi/dsi_manager.c | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c 
>> b/drivers/gpu/drm/msm/dsi/dsi_manager.c
>> index 3a1417397283..c4c24dabfd6f 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
>> @@ -450,6 +450,31 @@ static enum drm_mode_status 
>> dsi_mgr_bridge_mode_valid(struct drm_bridge *bridge,
>>       int id = dsi_mgr_bridge_get_id(bridge);
>>       struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
>>       struct mipi_dsi_host *host = msm_dsi->host;
>> +    struct platform_device *pdev = msm_dsi->pdev;
>> +    struct dev_pm_opp *opp;
>> +    unsigned long byte_clk_rate;
>> +
>> +    byte_clk_rate = dsi_byte_clk_get_rate(host, IS_BONDED_DSI(), mode);
>> +
>> +    /*
>> +     * If dev_pm_opp_find_freq_ceil() returns -EINVAL, its a bad
>> +     * pointer being passed, so treat as an error and return MODE_ERROR
>> +     *
>> +     * If dev_pm_opp_find_freq_ceil() returns -ERANGE, no clock
>> +     * was found matching the byte_clk, so return MODE_CLOCK_RANGE
>> +     *
>> +     * If dev_pm_opp_find_freq_ceil() returns -ENODEV, don't treat
>> +     * it as an error as it could mean opp table is not implemented
>> +     */
> 
> I'd say, too lengthy and verbose.
> 
hmmm .... just wanted to document the basis of the policy, I can make it 
shorter.

>> +    opp = dev_pm_opp_find_freq_ceil(&pdev->dev, &byte_clk_rate);
>> +    if (IS_ERR(opp)) {
>> +        if (PTR_ERR(opp) == -EINVAL)
>> +            return MODE_ERROR;
>> +        else if (PTR_ERR(opp) == -ERANGE)
>> +            return MODE_CLOCK_RANGE;
> 
> I think the logic should be quite opposite. Ignore -ENODEV, handle 
> -ERANGE and return MODE_ERROR for all other errors. In your code you are 
> ignoring not only -ENODEV, but all other possible errors which can be 
> added in future.
> 

Atm, those were the only ones handled but you are right.

this is better.

if (IS_ERR(opp)) {
	if (PTR_ERR(opp) == -ERANGE)
		return MODE_CLOCK_RANGE;
	else
		return MODE_ERROR;
} else {
	dev_pm_opp_put(opp);
}

>> +    } else {
>> +        dev_pm_opp_put(opp);
>> +    }
>>       return msm_dsi_host_check_dsc(host, mode);
>>   }
>