linux-kernel - Re: [PATCH v4 RESEND] pwm: atmel: add Timer Counter Block PWM driver

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Date:	Tue, 08 Jan 2013 13:43:56 +0100
From:	Boris BREZILLON <linux-arm@...rkiz.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
CC:	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Andrew Victor <linux@...im.org.za>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>
Subject: Re: [PATCH v4 RESEND] pwm: atmel: add Timer Counter Block PWM driver

On 08/01/2013 08:10, Thierry Reding wrote:
> On Thu, Dec 20, 2012 at 10:12:56AM +0100, Boris BREZILLON wrote:
>> Hi,
>>
>> Sorry for resend. The previous version still has alignment issues on 
>> atmel_tcb_pwm_set_polarity, atmel_tcb_pwm_request and
>> atmel_tcb_pwm_config function parameters.
>>
>> This patch adds a PWM driver based on Atmel Timer Counter Block.
>> Timer Counter Block is used in Waveform generator mode.
>>
>> A Timer Counter Block provides up to 6 PWM devices grouped by 2:
>> * group 0 = PWM 0 and 1
>> * group 1 = PWM 1 and 2
>> * group 2 = PMW 3 and 4
> 
> Should this be "PWM 2 and 3" and "PWM 4 and 5"? Or is PWM 1 shared
> between groups 0 and 1?
This is a mistake, this should be:
* group 0 = PWM 0 and 1
* group 1 = PWM 2 and 3
* group 2 = PMW 4 and 5
> 
>> +static int atmel_tcb_pwm_request(struct pwm_chip *chip,
>> +				 struct pwm_device *pwm)
>> +{
> [...]
>> +	clk_enable(tc->clk[group]);
> 
> You need to check the return value of clk_enable(). There's always a
> small possibility that it may fail.
> 
>> +static void atmel_tcb_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>> +{
> [...]
>> +	/* If duty is 0 reverse polarity */
>> +	if (tcbpwm->duty == 0)
>> +		polarity = !polarity;
> 
> Rather than commenting on what the code does, this should say why it
> does so.
> 

Is this an acceptable explanation ?

	/*
	 * If duty is 0 the timer will be stopped and we have to
	 * configure the output correctly on software trigger:
	 *  - set output to high if PWM_POLARITY_INVERSED
	 *  - set output to low if PWM_POLARITY_NORMAL
	 *
	 * This is why we're reverting polarity in this case.
	 */
>> +static int atmel_tcb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
>> +{
> [...]
>> +	/* If duty is 0 reverse polarity */
>> +	if (tcbpwm->duty == 0)
>> +		polarity = !polarity;
> 
> Same here.
> 
>> +static int atmel_tcb_pwm_probe(struct platform_device *pdev)
>> +{
> [...]
>> +	struct atmel_tcb_pwm_chip *tcbpwm;
>> +	struct device_node *np = pdev->dev.of_node;
>> +	struct atmel_tc *tc;
>> +	int err;
>> +	int tcblock;
>> +
>> +	err = of_property_read_u32(np, "tc-block", &tcblock);
>> +	if (err < 0) {
>> +		dev_err(&pdev->dev,
>> +			"failed to get tc block number from device tree (error: %d)\n",
> 
> Maybe: "failed to get Timer Counter Block number..." to make it
> consistent with the error message below:
> 
>> +	tc = atmel_tc_alloc(tcblock, "tcb-pwm");
>> +	if (tc == NULL) {
>> +		dev_err(&pdev->dev, "failed to allocate Timer Counter Block\n");
>> +		return -ENOMEM;
>> +	}
> [...]
>> +static const struct of_device_id atmel_tcb_pwm_dt_ids[] = {
>> +	{ .compatible = "atmel,tcb-pwm", },
>> +	{ /* sentinel */ }
>> +};
>> +MODULE_DEVICE_TABLE(of, mxs_pwm_dt_ids);
> 
> This is still wrong.
> 
>> +static struct platform_driver atmel_tcb_pwm_driver = {
>> +	.driver = {
>> +		.name = "atmel-tcb-pwm",
>> +		.of_match_table = atmel_tcb_pwm_dt_ids,
>> +	},
>> +	.probe = atmel_tcb_pwm_probe,
>> +	.remove = atmel_tcb_pwm_remove,
>> +};
>> +module_platform_driver(atmel_tcb_pwm_driver);
>> +
>> +MODULE_AUTHOR("Boris BREZILLON <b.brezillon@...rkiz.com>");
>> +MODULE_DESCRIPTION("Atmel Timer Counter Pulse Width Modulation Driver");
>> +MODULE_ALIAS("platform:atmel-tcb-pwm");
> 
> I don't think you needMODULE_ALIAS() if the alias is the same as the
> driver name.
> 
> Thierry
> 
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