Re: [PATCH v2 1/3] pwm: tegra: Make use of dev_err_probe()

[Uwe Kleine-König]

Hello Thierry,

On Mon, Sep 21, 2026 at 11:38:41AM +0200, Thierry Reding wrote:
> On Fri, Sep 18, 2026 at 04:33:45PM +0200, Uwe Kleine-König wrote:
> > Usage of dev_err_probe() is more compact than dev_err()'s, emits the
> > error code and handles -ENOMEM and -EPROBE_DEFER properly. Benefit from
> > these improvements.
> > 
> > Also add a few messages in error paths that lacked an output before.
> > 
> > Reviewed-by: Mikko Perttunen <mperttunen@xxxxxxxxxx>
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxx>
> > ---
> >  drivers/pwm/pwm-tegra.c | 52 ++++++++++++++++++++++++-----------------
> >  1 file changed, 31 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c
> > index 5cdbe120ba2d..efb7ab60f602 100644
> > --- a/drivers/pwm/pwm-tegra.c
> > +++ b/drivers/pwm/pwm-tegra.c
> > @@ -316,14 +316,15 @@ static const struct pwm_ops tegra_pwm_ops = {
> >  
> >  static int tegra_pwm_probe(struct platform_device *pdev)
> >  {
> > +	struct device *dev = &pdev->dev;
> >  	struct pwm_chip *chip;
> >  	struct tegra_pwm_chip *pc;
> >  	const struct tegra_pwm_soc *soc;
> >  	int ret;
> >  
> > -	soc = of_device_get_match_data(&pdev->dev);
> > +	soc = of_device_get_match_data(dev);
> >  
> > -	chip = devm_pwmchip_alloc(&pdev->dev, soc->num_channels, sizeof(*pc));
> > +	chip = devm_pwmchip_alloc(dev, soc->num_channels, sizeof(*pc));
> >  	if (IS_ERR(chip))
> >  		return PTR_ERR(chip);
> >  	pc = to_tegra_pwm_chip(chip);
> > @@ -331,28 +332,39 @@ static int tegra_pwm_probe(struct platform_device *pdev)
> >  	pc->soc = soc;
> >  
> >  	pc->regs = devm_platform_ioremap_resource(pdev, 0);
> > -	if (IS_ERR(pc->regs))
> > +	if (IS_ERR(pc->regs)) {
> > +		/*
> > +		 * devm_platform_ioremap_resource() already emits an error
> > +		 * message with CONFIG_HAS_IOMEM, so don't emit another message
> > +		 * here.
> > +		 */
> 
> Seems a bit counter-productive to leave comments like this. Function
> comments should document what the function does and then people should
> read those comments. Then we don't need to mention it every time we call
> these functions.

I often deal with bug reports by users where things fail without an
error message[1]. So a usual thing I do is checking probe (and other)
functions for silent error paths. As I fail to follow the (continously
changing) set of functions that emit an error message, this comment is
very useful for a me at least and I'd wish others would add such
comments, too. (An IMHO fine thing here would be to let no generic
resource getter function emit an error message, but that ship has
sailed.)

I'd be open for a shorter marker, that might even be machine-parsable.
 
> >  		return PTR_ERR(pc->regs);
> > +	}
> >  
> >  	platform_set_drvdata(pdev, chip);
> >  
> > -	pc->clk = devm_clk_get(&pdev->dev, NULL);
> > +	pc->clk = devm_clk_get(dev, NULL);
> >  	if (IS_ERR(pc->clk))
> > -		return PTR_ERR(pc->clk);
> > +		return dev_err_probe(dev, PTR_ERR(pc->clk), "Failed to get clock\n");
> >  
> > -	ret = devm_tegra_core_dev_init_opp_table_common(&pdev->dev);
> > -	if (ret)
> > +	ret = devm_tegra_core_dev_init_opp_table_common(dev);
> > +	if (ret) {
> > +		/*
> > +		 * devm_tegra_core_dev_init_opp_table_common() emits an error
> > +		 * message most of the time, so don't add another.
> > +		 */
> 
> Same here.
> 
> > @@ -385,17 +395,17 @@ static int tegra_pwm_probe(struct platform_device *pdev)
> >  
> >  	ret = pwmchip_add(chip);
> >  	if (ret < 0) {
> > -		dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
> > +		dev_err_probe(dev, ret, "Adding pwmchip failed\n");
> 
> This stands out as very different from other error messages, so maybe
> change this to something like "Failed to add PWM chip" for consistency?

Fine for me, will fix in the next submission.

Thanks for your feedback,
Uwe

[1] last instance was just today, where on a bananapi USB didn't work
    and /sys/kernel/debug/devices_deferred ended up containing:

	1c13000.usb     platform: supplier 1c13400.phy not ready
	1c1c000.usb     platform: supplier 1c13400.phy not ready
	1c14400.usb     platform: supplier 1c13400.phy not ready
	1c13400.phy     platform: supplier axp20x-usb-power-supply not ready
	1c14000.usb     platform: supplier 1c13400.phy not ready
	1c1c400.usb     platform: supplier 1c13400.phy not ready
	axp20x-usb-power-supply

    It would be so easy[2] to add a useful debugging hint here

[2] https://lore.kernel.org/all/b699f8251afed736af454a981630926e45eb7da7.1789983244.git.ukleinek@xxxxxxxxxx/

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