ASoC: rsnd: adg: clearly handle clock error / NULL case

From: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>

This driver is assuming that all adg->clk[i] is not NULL.
Because of this prerequisites, for_each_rsnd_clk() is possible to work
for all clk without checking NULL. In other words, all adg->clk[i]
should not NULL.

Some SoC might doesn't have clk_a/b/c/i. devm_clk_get() returns error in
such case. This driver calls rsnd_adg_null_clk_get() and use null_clk
instead of NULL in such cases.

But devm_clk_get() might returns NULL even though such clocks exist, but
it doesn't mean error (user deliberately chose to disable the feature).
NULL clk itself is not error from clk point of view, but is error from
this driver point of view because it is not assuming such case.

But current code is using IS_ERR() which doesn't care NULL.
This driver uses IS_ERR_OR_NULL() instead of IS_ERR() for clk check.
And it uses ERR_CAST() to clarify null_clk error.

One concern here is that it unconditionally uses null_clk if clk_a/b/c/i
was error. It is correct if it doesn't exist, but is not correct if it
returns error even though it exist.
It needs to check "clock-names" from DT before calling devm_clk_get() to
handling such case. But let's assume it is overkill so far.

Link: https://lore.kernel.org/r/YMCmhfQUimHCSH/n@mwanda
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
---
 sound/soc/sh/rcar/adg.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

On Fri, Jun 11, 2021 at 08:23:28AM +0900, Kuninori Morimoto wrote:
> 
> From: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
> 
> This driver is assuming that all adg->clk[i] is not NULL.
> Because of this prerequisites, for_each_rsnd_clk() is possible to work
> for all clk without checking NULL. In other words, all adg->clk[i]
> should not NULL.
> 
> Some SoC might doesn't have clk_a/b/c/i. devm_clk_get() returns error in
> such case. This driver calls rsnd_adg_null_clk_get() and use null_clk
> instead of NULL in such cases.
> 
> But devm_clk_get() might returns NULL even though such clocks exist, but
> it doesn't mean error (user deliberately chose to disable the feature).
> NULL clk itself is not error from clk point of view, but is error from
> this driver point of view because it is not assuming such case.
> 
> But current code is using IS_ERR() which doesn't care NULL.
> This driver uses IS_ERR_OR_NULL() instead of IS_ERR() for clk check.
> And it uses ERR_CAST() to clarify null_clk error.
> 
> One concern here is that it unconditionally uses null_clk if clk_a/b/c/i
> was error. It is correct if it doesn't exist, but is not correct if it
> returns error even though it exist.
> It needs to check "clock-names" from DT before calling devm_clk_get() to
> handling such case. But let's assume it is overkill so far.
> 
> Link: https://lore.kernel.org/r/YMCmhfQUimHCSH/n@mwanda 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
> ---
>  sound/soc/sh/rcar/adg.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/soc/sh/rcar/adg.c b/sound/soc/sh/rcar/adg.c
> index 0ebee1ed06a9..abe9d539709b 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 ERR_CAST(clk);
>  	}
>  
>  	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))

"clk" can't be NULL here, right?  So this should just be:

	if (IS_ERR(clk))

(because when a function returns NULL it shouldn't print an error)

regards,
dan carpenter

Hi Dan

Thank you for your feedback

> > @@ -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))
> 
> "clk" can't be NULL here, right?  So this should just be:
> 
> 	if (IS_ERR(clk))

clk_register_fixed_rate() might return NULL ?
I'm not sure detail.
It is indicating that "error / NULL are both error on this driver".

> (because when a function returns NULL it shouldn't print an error)

It is "from clk framework point of view" right ?
This driver doesn't assume "NULL clk" for any case.

Thank you for your help !!

Best regards
---
Kuninori Morimoto