Re: [PATCH] drivers: thermal: tsens: Work with old DTBs

[Stephan Gerhold <stephan@gerhold.net>]

Hi Amit,

Thanks for the patch!

On Wed, Dec 11, 2019 at 03:28:33PM +0530, Amit Kucheria wrote:
> In order for the old DTBs to continue working, the new interrupt code
> must not return an error if interrupts are not defined.
> 
> Fixes: 634e11d5b450a ("drivers: thermal: tsens: Add interrupt support")
> Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
> ---
>  drivers/thermal/qcom/tsens.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
> index 015e7d2015985..d8f51067ed411 100644
> --- a/drivers/thermal/qcom/tsens.c
> +++ b/drivers/thermal/qcom/tsens.c
> @@ -109,7 +109,7 @@ static int tsens_register(struct tsens_priv *priv)
>  
>  	irq = platform_get_irq_byname(pdev, "uplow");
>  	if (irq < 0) {
> -		ret = irq;
> +		dev_warn(&pdev->dev, "Missing uplow irq in DT\n");
>  		goto err_put_device;
>  	}

platform_get_irq_byname() already logs an error if the IRQ cannot be
found: qcom-tsens 4a9000.thermal-sensor: IRQ uplow not found

To replace that error with a warning (not sure if that is worth it),
we would need to replace the call with platform_get_irq_byname_optional().

>  
> @@ -118,7 +118,8 @@ static int tsens_register(struct tsens_priv *priv)
>  					IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
>  					dev_name(&pdev->dev), priv);
>  	if (ret) {
> -		dev_err(&pdev->dev, "%s: failed to get irq\n", __func__);
> +		dev_warn(&pdev->dev, "%s: failed to get uplow irq\n", __func__);
> +		ret = 0;
>  		goto err_put_device;

In case of the old DT, platform_get_irq_byname() will return -ENXIO,
because no interrupt is specified in the device tree.
So we should have already run into the error earlier,
and jumped to "err_put_device".

Is this hunk really necessary?

In other words, wouldn't it be enough to do something like

@@ -110,6 +110,8 @@ static int tsens_register(struct tsens_priv *priv)
 	irq = platform_get_irq_byname(pdev, "uplow");
 	if (irq < 0) {
 		ret = irq;
+		if (ret == -ENXIO)
+			ret = 0;
 		goto err_put_device;
 	}

... to essentially ignore only the "IRQ does not exist" condition
for old device trees?

Thanks,
Stephan