linux-kernel - Re: [PATCH v1 1/5] pwm: mediatek: add a property "mediatek,num-pwms"

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Date:   Mon, 21 Jan 2019 09:49:48 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Ryder Lee <ryder.lee@...iatek.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        Sean Wang <sean.wang@...nel.org>,
        Weijie Gao <weijie.gao@...iatek.com>,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 1/5] pwm: mediatek: add a property "mediatek,num-pwms"

On Sat, Jan 19, 2019 at 10:54:47AM +0800, Ryder Lee wrote:
> On Fri, 2019-01-18 at 09:43 +0100, Matthias Brugger wrote:
> > 
> > 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@...iatek.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.
> 
> I'm not sure how to properly curve it out? I think we still need this
> variable to save the specific value for some legacy SoCs (with older
> DTs).

I guess he means  something like:

	if (is_compatible_to_variant_A(dev))
		num_pwms = 12;
	else if (is_compatible_to_variant_B(dev))
		num_pwms = 2;

. In my eyes the bike shed should be light red and I prefer to collect
the fallback num_pwms in the compatible_data as is to keep the code
simpler. Maybe rename the member from num_pwms to fallback_num_pwms to
make it more obvious that it doesn't represent the actually used value.

> > With a expressive comment it will help other driver developers to not start
> > adding num_pwms in the platform data in their first attempt.
> 
> Definitely.

My suggestion was to add a dev_warn, which IMHO is still better than a
comment.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |