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Subject: Re: [PATCH v1 1/5] pwm: mediatek: add a property "mediatek,num-pwms"
To:     Ryder Lee <ryder.lee@mediatek.com>,
        Thierry Reding <thierry.reding@gmail.com>
Cc:     linux-pwm@vger.kernel.org, devicetree@vger.kernel.org,
        Sean Wang <sean.wang@kernel.org>,
        Weijie Gao <weijie.gao@mediatek.com>,
        linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org
References: <de316385a84e079d3b23891e61c959094b9fa7e5.1547781007.git.ryder.lee@mediatek.com>
From:   Matthias Brugger <matthias.bgg@gmail.com>
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Message-ID: <c007d399-af86-98d3-94f9-b9762efdc219@gmail.com>
Date:   Fri, 18 Jan 2019 09:43:53 +0100
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In-Reply-To: <de316385a84e079d3b23891e61c959094b9fa7e5.1547781007.git.ryder.lee@mediatek.com>
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On 18/01/2019 04:24, Ryder Lee wrote:
> This adds a property "mediatek,num-pwms" to avoid having an endless
> list of compatibles with no differences for the same driver.
> 
> Thus, the driver should have backwards compatibility to older DTs.
> 
> Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
> ---
> Changes since v1: add some checks for backwards compatibility.
> ---
>  drivers/pwm/pwm-mediatek.c | 27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c
> index eb6674c..81b7e5e 100644
> --- a/drivers/pwm/pwm-mediatek.c
> +++ b/drivers/pwm/pwm-mediatek.c
> @@ -55,7 +55,7 @@ enum {
>  };
>  
>  struct mtk_pwm_platform_data {
> -	unsigned int num_pwms;
> +	unsigned int num_pwms;	/* it should not be used in the future SoCs */
>  	bool pwm45_fixup;
>  	bool has_clks;
>  };
> @@ -226,27 +226,36 @@ static void mtk_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>  
>  static int mtk_pwm_probe(struct platform_device *pdev)
>  {
> -	const struct mtk_pwm_platform_data *data;
> +	struct device_node *np = pdev->dev.of_node;
>  	struct mtk_pwm_chip *pc;
>  	struct resource *res;
> -	unsigned int i;
> +	unsigned int i, num_pwms;
>  	int ret;
>  
>  	pc = devm_kzalloc(&pdev->dev, sizeof(*pc), GFP_KERNEL);
>  	if (!pc)
>  		return -ENOMEM;
>  
> -	data = of_device_get_match_data(&pdev->dev);
> -	if (data == NULL)
> -		return -EINVAL;
> -	pc->soc = data;
> +	pc->soc = of_device_get_match_data(&pdev->dev);
>  
>  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>  	pc->regs = devm_ioremap_resource(&pdev->dev, res);
>  	if (IS_ERR(pc->regs))
>  		return PTR_ERR(pc->regs);
>  
> -	for (i = 0; i < data->num_pwms + 2 && pc->soc->has_clks; i++) {
> +	/* Check if we have set 'num-pwms' in DTs. */
> +	ret = of_property_read_u32(np, "mediatek,num-pwms", &num_pwms);
> +	if (ret < 0) {
> +		/* If no, fallback to use SoC data for backwards compatibility. */
> +		if (pc->soc->num_pwms) {
> +			num_pwms = pc->soc->num_pwms;

Maybe that's bike shedding, but I think it would be better to carve out the
num_pwms from the mtk_pwm_platform_data and check against the compatible here.
With a expressive comment it will help other driver developers to not start
adding num_pwms in the platform data in their first attempt.

Regards,
Matthias

> +		} else {
> +			dev_err(&pdev->dev, "failed to get pwm number: %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	for (i = 0; i < num_pwms + 2 && pc->soc->has_clks; i++) {
>  		pc->clks[i] = devm_clk_get(&pdev->dev, mtk_pwm_clk_name[i]);
>  		if (IS_ERR(pc->clks[i])) {
>  			dev_err(&pdev->dev, "clock: %s fail: %ld\n",
> @@ -260,7 +269,7 @@ static int mtk_pwm_probe(struct platform_device *pdev)
>  	pc->chip.dev = &pdev->dev;
>  	pc->chip.ops = &mtk_pwm_ops;
>  	pc->chip.base = -1;
> -	pc->chip.npwm = data->num_pwms;
> +	pc->chip.npwm = num_pwms;
>  
>  	ret = pwmchip_add(&pc->chip);
>  	if (ret < 0) {
>