[bug report] ASoC: rsnd: add null CLOCKIN support

[Dan Carpenter]

On Thu, Jun 10, 2021 at 08:31:25AM +0900, Kuninori Morimoto wrote:
> 
> Hi Dan
> 
> Thank you for your research.
> 
> > sound/soc/sh/rcar/adg.c
> >    423  static int rsnd_adg_get_clkin(struct rsnd_priv *priv)
> >    424  {
> >    425          struct rsnd_adg *adg = priv->adg;
> >    426          struct device *dev = rsnd_priv_to_dev(priv);
> >    427          struct clk *clk;
> >    428          int i;
> >    429  
> >    430          for (i = 0; i < CLKMAX; i++) {
> >    431                  clk = devm_clk_get(dev, clk_name[i]);
> > 
> > If devm_clk_get() returns NULL that's not an error.
> > 
> > 
> >    432  
> >    433                  if (IS_ERR(clk))
> >    434                          clk = rsnd_adg_null_clk_get(priv);
> > 
> > But I think if rsnd_adg_null_clk_get() returns an error then it is an
> > error.
> > 
> > 
> >    435                  if (IS_ERR(clk))
> > 
> > This is impossible.
> > 
> >    436                          goto err;
> > 
> > So I think it should be:
> > 
> > 			if (IS_ERR(clk)) {
> > 				clk = rsnd_adg_null_clk_get(priv);
> > 				if (!clk)
> > 					goto err;
> > 			}
> 
> Hmm indeed. Thank you for your report, I didn't notice about it.
> How about this ?
> 
> ----------
> diff --git a/sound/soc/sh/rcar/adg.c b/sound/soc/sh/rcar/adg.c
> index 0ebee1ed06a9..2b05a1568ee8 100644
> --- a/sound/soc/sh/rcar/adg.c
> +++ b/sound/soc/sh/rcar/adg.c
> @@ -393,7 +393,7 @@ static struct clk *rsnd_adg_create_null_clk(struct rsnd_priv *priv,
>  	clk = clk_register_fixed_rate(dev, name, parent, 0, 0);
>  	if (IS_ERR(clk)) {
>  		dev_err(dev, "create null clk error\n");
> -		return NULL;
> +		return PTR_ERR(clk);

Yes, I think this part is correct.  If an error happens, then it should
be reported to the user so they can fix it.

>  	}
>  
>  	return clk;
> @@ -430,9 +430,9 @@ static int rsnd_adg_get_clkin(struct rsnd_priv *priv)
>  	for (i = 0; i < CLKMAX; i++) {
>  		clk = devm_clk_get(dev, clk_name[i]);
>  
> -		if (IS_ERR(clk))
> +		if (IS_ERR_OR_NULL(clk))
>  			clk = rsnd_adg_null_clk_get(priv);
> -		if (IS_ERR(clk))
> +		if (IS_ERR_OR_NULL(clk))
>  			goto err;

But this is not correct.

If a function like devm_clk_get() returns NULL, then it's not an error,
it's something where the user deliberately chose to disable the feature.
It shouldn't trigger an error message and the rest of the driver should
be written to accomodate it.

>  
>  		adg->clk[i] = clk;

So we should assign the NULL pointer here and add NULL checks to make
sure that it doesn't lead to a NULL dereference.

regards,
dan carpenter