linux-kernel - Re: [PATCH 1/6] serial: 8250

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Message-ID: <BLU0-SMTP18236DF570FFD5F879EC61B8AEE0@phx.gbl>
Date:	Fri, 15 Mar 2013 21:40:47 -0300
From:	Emilio López <emilio@...pez.com.ar>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	sunny@...winnertech.com, shuge@...winnertech.com,
	Jiri Slaby <jslaby@...e.cz>, kevin@...winnertech.com
Subject: Re: [PATCH 1/6] serial: 8250_dw: add support for clk api

El 15/03/13 21:29, Russell King - ARM Linux escribió:
> On Fri, Mar 15, 2013 at 09:15:11PM -0300, Emilio López wrote:
>> Hello Russell,
>>
>> El 15/03/13 19:39, Russell King - ARM Linux escribió:
>>> On Fri, Mar 15, 2013 at 09:06:23PM +0100, Maxime Ripard wrote:
>>>> +	/* clock got configured through clk api, all done */
>>>> +	if (p->uartclk)
>>>
>>> 	if (IS_ERR(p->uartclk))
>>>
>>
>> Isn't IS_ERR for pointers? p->uartclk is an unsigned int
> 
> Right, sorry, ignore that.
> 
>>>> +		return 0;
>>>> +
>>>> +	/* try to find out clock frequency from DT as fallback */
>>>>  	if (of_property_read_u32(np, "clock-frequency", &val)) {
>>>> -		dev_err(p->dev, "no clock-frequency property set\n");
>>>> +		dev_err(p->dev, "clk or clock-frequency not defined\n");
>>>>  		return -EINVAL;
>>>>  	}
>>>>  	p->uartclk = val;
>>>> @@ -294,9 +301,21 @@ static int dw8250_probe(struct platform_device *pdev)
>>>>  	if (!uart.port.membase)
>>>>  		return -ENOMEM;
>>>>  
>>>> +	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
>>>> +	if (!data)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	data->clk = devm_clk_get(&pdev->dev, NULL);
>>>> +	if (IS_ERR(data->clk))
>>>> +		data->clk = NULL;
>>>> +	else
>>>> +		clk_prepare_enable(data->clk);
>>>
>>> 	if (!IS_ERR(data->clk))
>>> 		clk_prepare_enable(data->clk);
>>>
>>
>> See below
>>
>>>> +
>>>>  	uart.port.iotype = UPIO_MEM;
>>>>  	uart.port.serial_in = dw8250_serial_in;
>>>>  	uart.port.serial_out = dw8250_serial_out;
>>>> +	uart.port.private_data = data;
>>>> +	uart.port.uartclk = clk_get_rate(data->clk);
>>>
>>> What if data->clk is invalid?
>>>
>>> 	if (!IS_ERR(data->clk)
>>> 		uart.port.uartclk = clk_get_rate(data->clk);
>>>
>>
>> I'm not sure if it is coincidental or the way it is supposed to be, but
>> when using the common clock framework, if you pass a NULL to
>> clk_get_rate, the function explicitly checks for it and returns 0. I
>> relied on that behaviour when implementing this; see the if..else block
>> above. Is this not always the case on other clock drivers?
> 
> That's something that the common clock framework decided to do.  It's
> not a defined part of the API though, so drivers shouldn't rely on
> this behaviour meaning anything special.

Ok then, I'll rework the error checking on the clock calls and get a new
patch sent. Thanks for the clarification.

Emilio
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