Re: [PATCH 3/4] [resend #2] fb_ddc: Allow I2C adapters without SCL read capability

[Tomi Valkeinen]

On 02/09/15 15:04, Ondrej Zary wrote:
> On Wednesday 02 September 2015, Tomi Valkeinen wrote:
>> On 24/08/15 22:37, Ondrej Zary wrote:
>>> i2c-algo-bit allows I2C adapters without SCL read capability to work but
>>> fb_ddc_read fails to work on them.
>>>
>>> Fix fb_ddc_read to work with I2C adapters not capable of reading SCL.
>>>
>>> Signed-off-by: Ondrej Zary <linux@xxxxxxxxxxxxxxxxxxxx>
>>> Acked-by: Krzysztof Helt <krzysztof.h1@xxxxx>
>>> ---
>>>  drivers/video/fbdev/core/fb_ddc.c |    8 +++++---
>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/video/fbdev/core/fb_ddc.c
>>> b/drivers/video/fbdev/core/fb_ddc.c index 94322cc..22c694a 100644
>>> --- a/drivers/video/fbdev/core/fb_ddc.c
>>> +++ b/drivers/video/fbdev/core/fb_ddc.c
>>> @@ -69,10 +69,11 @@ unsigned char *fb_ddc_read(struct i2c_adapter
>>> *adapter) algo_data->setscl(algo_data->data, 1);
>>>  		for (j = 0; j < 5; j++) {
>>>  			msleep(10);
>>> -			if (algo_data->getscl(algo_data->data))
>>> +			if (algo_data->getscl &&
>>> +			    algo_data->getscl(algo_data->data))
>>>  				break;
>>>  		}
>>> -		if (j == 5)
>>> +		if (algo_data->getscl && j == 5)
>>>  			continue;
>>>
>>>  		algo_data->setsda(algo_data->data, 0);
>>> @@ -91,7 +92,8 @@ unsigned char *fb_ddc_read(struct i2c_adapter *adapter)
>>>  		algo_data->setscl(algo_data->data, 1);
>>>  		for (j = 0; j < 10; j++) {
>>>  			msleep(10);
>>> -			if (algo_data->getscl(algo_data->data))
>>> +			if (algo_data->getscl &&
>>> +			    algo_data->getscl(algo_data->data))
>>>  				break;
>>>  		}
>>
>> Aren't both of those loops pointless if there's no getscl?
> 
> They're reduced to delays - don't know how much critical they are.

I think the code gets somewhat confusing the way you did it.

Maybe instead something like:

if (algo_data->getscl) {
	the current loop & delays here;
} else {
	msleep(25); // 25 was just a guess...
}

 Tomi

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