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Subject: Re: [PATCH 1/5] pwm: mediatek: add a property "mediatek,num-pwms"
To:     Ryder Lee <ryder.lee@mediatek.com>,
        Thierry Reding <thierry.reding@gmail.com>
Cc:     Sean Wang <sean.wang@kernel.org>,
        Weijie Gao <weijie.gao@mediatek.com>,
        linux-pwm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
References: <0c400cb1899c1afb4c9f021350cdc0c6ca3f6239.1547453586.git.ryder.lee@mediatek.com>
From:   Matthias Brugger <matthias.bgg@gmail.com>
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Message-ID: <0546d8b6-ac67-d445-677a-ff888edf9646@gmail.com>
Date:   Mon, 14 Jan 2019 12:16:39 +0100
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On 14/01/2019 09:21, Ryder Lee wrote:
> This adds a property "mediatek,num-pwms" to avoid having an endless
> list of compatibles with no other differences for the same driver.
> 
> Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
> ---
>  drivers/pwm/pwm-mediatek.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c
> index eb6674c..37daa84 100644
> --- a/drivers/pwm/pwm-mediatek.c
> +++ b/drivers/pwm/pwm-mediatek.c
> @@ -55,7 +55,6 @@ enum {
>  };
>  
>  struct mtk_pwm_platform_data {
> -	unsigned int num_pwms;
>  	bool pwm45_fixup;
>  	bool has_clks;
>  };
> @@ -226,10 +225,11 @@ static void mtk_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>  
>  static int mtk_pwm_probe(struct platform_device *pdev)
>  {
> +	struct device_node *np = pdev->dev.of_node;
>  	const struct mtk_pwm_platform_data *data;
>  	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);
> @@ -246,7 +246,13 @@ static int mtk_pwm_probe(struct platform_device *pdev)
>  	if (IS_ERR(pc->regs))
>  		return PTR_ERR(pc->regs);
>  
> -	for (i = 0; i < data->num_pwms + 2 && pc->soc->has_clks; i++) {
> +	ret = of_property_read_u32(np, "mediatek,num-pwms", &num_pwms);
> +	if (ret < 0) {
> +		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 +266,7 @@ 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) {
> @@ -279,32 +285,23 @@ static int mtk_pwm_remove(struct platform_device *pdev)
>  }
>  
>  static const struct mtk_pwm_platform_data mt2712_pwm_data = {
> -	.num_pwms = 8,
> -	.pwm45_fixup = false,
> -	.has_clks = true,
> -};
> -
> -static const struct mtk_pwm_platform_data mt7622_pwm_data = {
> -	.num_pwms = 6,
>  	.pwm45_fixup = false,
>  	.has_clks = true,
>  };

From my point of view that's not perfect. We should make sure that a newer
kernel does not break with an older device tree and vice versa.
Just imagine I use some board where u-boot passes the device tree to the kernel,
I update the kernel and PWM is broken.

So also it is crappy we will need to have the num_pwms variable for the older
boards.
Maybe put a switch in the probe function which checks the compatible with a
comment message saying that this is for legacy device tree, so that no new
contributer just copys the wrong code.

What do you think?
Regards,
Matthias

>  
>  static const struct mtk_pwm_platform_data mt7623_pwm_data = {
> -	.num_pwms = 5,
>  	.pwm45_fixup = true,
>  	.has_clks = true,
>  };
>  
>  static const struct mtk_pwm_platform_data mt7628_pwm_data = {
> -	.num_pwms = 4,
>  	.pwm45_fixup = true,
>  	.has_clks = false,
>  };
>  
>  static const struct of_device_id mtk_pwm_of_match[] = {
>  	{ .compatible = "mediatek,mt2712-pwm", .data = &mt2712_pwm_data },
> -	{ .compatible = "mediatek,mt7622-pwm", .data = &mt7622_pwm_data },
> +	{ .compatible = "mediatek,mt7622-pwm", .data = &mt2712_pwm_data },
>  	{ .compatible = "mediatek,mt7623-pwm", .data = &mt7623_pwm_data },
>  	{ .compatible = "mediatek,mt7628-pwm", .data = &mt7628_pwm_data },
>  	{ },
>