linux-kernel - Re: [PATCH] drm/dsi: Fix improper use of mipi_dsi_device

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Date:   Mon, 15 Jan 2018 13:42:00 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Archit Taneja <architt@...eaurora.org>,
        Brian Norris <briannorris@...omium.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Vincent ABRIOU <vincent.abriou@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>
Subject: Re: [PATCH] drm/dsi: Fix improper use of mipi_dsi_device_transfer()
 return value

Hi Andrzej,

On 01/15/2018 10:12 AM, Andrzej Hajda wrote:
> On 12.01.2018 15:48, Philippe Cornu wrote:
>> The function mipi_dsi_device_transfer() returns the number of transmitted
>> or received bytes on success or a negative error code on failure.
>>
>> The functions mipi_dsi_shutdown_peripheral(), mipi_dsi_turn_on_peripheral() &
>> mipi_dsi_set_maximum_return_packet_size() use improperly this returned
>> value in case of success: 0 should be returned instead of the number of
>> transmitted bytes.
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
> 
> I guess, the best would be to create and use some helper similar to
> PTR_ERR_OR_ZERO,
> but this is also OK.
> 

Many thanks for your comment and review.

Before sending this patch, I searched for a better way to write these 
few lines, including searching for such macros but I did not find 
anything (pointers are largely covered but simple integers are not).

If someone has a better solution (with macros or otherwise), I am happy 
to learn/implement it.

Many thanks,
Philippe : )

> Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
> 
>   --
> Regards
> Andrzej
> 
>> ---
>>   drivers/gpu/drm/drm_mipi_dsi.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
>> index 4b47226b90d4..bc73b7f5b9fc 100644
>> --- a/drivers/gpu/drm/drm_mipi_dsi.c
>> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
>> @@ -498,8 +498,9 @@ int mipi_dsi_shutdown_peripheral(struct mipi_dsi_device *dsi)
>>   		.tx_buf = (u8 [2]) { 0, 0 },
>>   		.tx_len = 2,
>>   	};
>> +	int ret = mipi_dsi_device_transfer(dsi, &msg);
>>   
>> -	return mipi_dsi_device_transfer(dsi, &msg);
>> +	return (ret < 0) ? ret : 0;
>>   }
>>   EXPORT_SYMBOL(mipi_dsi_shutdown_peripheral);
>>   
>> @@ -517,8 +518,9 @@ int mipi_dsi_turn_on_peripheral(struct mipi_dsi_device *dsi)
>>   		.tx_buf = (u8 [2]) { 0, 0 },
>>   		.tx_len = 2,
>>   	};
>> +	int ret = mipi_dsi_device_transfer(dsi, &msg);
>>   
>> -	return mipi_dsi_device_transfer(dsi, &msg);
>> +	return (ret < 0) ? ret : 0;
>>   }
>>   EXPORT_SYMBOL(mipi_dsi_turn_on_peripheral);
>>   
>> @@ -541,8 +543,9 @@ int mipi_dsi_set_maximum_return_packet_size(struct mipi_dsi_device *dsi,
>>   		.tx_len = sizeof(tx),
>>   		.tx_buf = tx,
>>   	};
>> +	int ret = mipi_dsi_device_transfer(dsi, &msg);
>>   
>> -	return mipi_dsi_device_transfer(dsi, &msg);
>> +	return (ret < 0) ? ret : 0;
>>   }
>>   EXPORT_SYMBOL(mipi_dsi_set_maximum_return_packet_size);
>>   
> 
>