Re: [PATCH v2] clk: let clk_disable() return immediately if clk is NULL or error

Re: [PATCH v2] clk: let clk_disable() return immediately if clk is NULL or error

[Ralf Baechle]

On Thu, Apr 07, 2016 at 05:33:28PM -0700, Stephen Boyd wrote:

> On 04/05, Masahiro Yamada wrote:
> > The clk_disable() in the common clock framework (drivers/clk/clk.c)
> > returns immediately if a given clk is NULL or an error pointer.  It
> > allows clock consumers to call clk_disable() without IS_ERR_OR_NULL
> > checking if drivers are only used with the common clock framework.
> > 
> > Unfortunately, NULL/error checking is missing from some of non-common
> > clk_disable() implementations.  This prevents us from completely
> > dropping NULL/error checking from callers.  Let's make it tree-wide
> > consistent by adding IS_ERR_OR_NULL(clk) to all callees.
> > 
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > Acked-by: Greg Ungerer <gerg@uclinux.org>
> > Acked-by: Wan Zongshun <mcuos.com@gmail.com>
> > ---
> > 
> > Stephen,
> > 
> > This patch has been unapplied for a long time.
> > 
> > Please let me know if there is something wrong with this patch.
> > 
> 
> I'm mostly confused why we wouldn't want to encourage people to
> call clk_disable or unprepare on a clk that's an error pointer.
> Typically an error pointer should be dealt with, instead of
> silently ignored, so why wasn't it dealt with by passing it up
> the probe() path?

While your argument makes perfect sense, Many clk_disable implementations
are already doing similar checks, for example:

arch/arm/mach-davinci/clock.c:

void clk_disable(struct clk *clk)
{
	unsigned long flags;

	if (clk == NULL || IS_ERR(clk))
		return;
[...]

arch/arm/mach-omap1/clock.c

void clk_disable(struct clk *clk)
{
        unsigned long flags;

        if (clk == NULL || IS_ERR(clk))
                return;
[...]

arch/avr32/mach-at32ap/clock.c

void clk_disable(struct clk *clk)
{
        unsigned long flags;

        if (IS_ERR_OR_NULL(clk))
                return;
[...]

arch/mips/lantiq/clk.c:

static inline int clk_good(struct clk *clk)
{
	return clk && !IS_ERR(clk);
}

[...]

void clk_disable(struct clk *clk)
{
	if (unlikely(!clk_good(clk)))
		return;

	if (clk->disable)
[...]

So should we go and weed out these checks?

  Ralf

Re: [PATCH v2] clk: let clk_disable() return immediately if clk is NULL or error

[Masahiro Yamada]

2016-04-08 19:06 GMT+09:00 Ralf Baechle <ralf@linux-mips.org>:
> On Thu, Apr 07, 2016 at 05:33:28PM -0700, Stephen Boyd wrote:
>
>> On 04/05, Masahiro Yamada wrote:
>> > The clk_disable() in the common clock framework (drivers/clk/clk.c)
>> > returns immediately if a given clk is NULL or an error pointer.  It
>> > allows clock consumers to call clk_disable() without IS_ERR_OR_NULL
>> > checking if drivers are only used with the common clock framework.
>> >
>> > Unfortunately, NULL/error checking is missing from some of non-common
>> > clk_disable() implementations.  This prevents us from completely
>> > dropping NULL/error checking from callers.  Let's make it tree-wide
>> > consistent by adding IS_ERR_OR_NULL(clk) to all callees.
>> >
>> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> > Acked-by: Greg Ungerer <gerg@uclinux.org>
>> > Acked-by: Wan Zongshun <mcuos.com@gmail.com>
>> > ---
>> >
>> > Stephen,
>> >
>> > This patch has been unapplied for a long time.
>> >
>> > Please let me know if there is something wrong with this patch.
>> >
>>
>> I'm mostly confused why we wouldn't want to encourage people to
>> call clk_disable or unprepare on a clk that's an error pointer.
>> Typically an error pointer should be dealt with, instead of
>> silently ignored, so why wasn't it dealt with by passing it up
>> the probe() path?
>
> While your argument makes perfect sense, Many clk_disable implementations
> are already doing similar checks, for example:
>
> arch/arm/mach-davinci/clock.c:
>
> void clk_disable(struct clk *clk)
> {
>         unsigned long flags;
>
>         if (clk == NULL || IS_ERR(clk))
>                 return;
> [...]
>
> arch/arm/mach-omap1/clock.c
>
> void clk_disable(struct clk *clk)
> {
>         unsigned long flags;
>
>         if (clk == NULL || IS_ERR(clk))
>                 return;
> [...]
>
> arch/avr32/mach-at32ap/clock.c
>
> void clk_disable(struct clk *clk)
> {
>         unsigned long flags;
>
>         if (IS_ERR_OR_NULL(clk))
>                 return;
> [...]
>
> arch/mips/lantiq/clk.c:
>
> static inline int clk_good(struct clk *clk)
> {
>         return clk && !IS_ERR(clk);
> }
>
> [...]
>
> void clk_disable(struct clk *clk)
> {
>         if (unlikely(!clk_good(clk)))
>                 return;
>
>         if (clk->disable)
> [...]
>
> So should we go and weed out these checks?
>
>   Ralf


Please help me understand your thought clearly.

[1] Should calling clk_unprepare/disable() with a NULL pointer be allowed?

[2] Should calling clk_unprepare/disable() with an error pointer be allowed?


-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2] clk: let clk_disable() return immediately if clk is NULL or error

[Stephen Boyd]

On 04/08, Ralf Baechle wrote:
> 
> While your argument makes perfect sense, Many clk_disable implementations
> are already doing similar checks, for example:
> 
> arch/arm/mach-davinci/clock.c:
> 
[...]
> 
> So should we go and weed out these checks?

Yes, it would be nice to at least make the differing
implementations of the clk API consistent. Of course, we should
really put our efforts towards getting rid of the non-CCF
implementations instead so that there's less confusion overall.

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