[PATCH 1/7] clk: Make rfree return void

[Simon Glass]

Hi Sean,

On Sun, 27 Feb 2022 at 12:38, Sean Anderson <seanga2 at gmail.com> wrote:
>
> On 2/26/22 1:36 PM, Simon Glass wrote:
> > Hi Sean,
> >
> > On Tue, 1 Feb 2022 at 21:24, Sean Anderson <seanga2 at gmail.com> wrote:
> >>
> >> On 2/1/22 10:59 PM, Simon Glass wrote:
> >>> Hi Sean,
> >>>
> >>> On Tue, 1 Feb 2022 at 07:49, Sean Anderson <seanga2 at gmail.com> wrote:
> >>>>
> >>>> On 1/27/22 4:35 PM, Simon Glass wrote:
> >>>>> Hi Sean,
> >>>>>
> >>>>> On Thu, 27 Jan 2022 at 08:43, Sean Anderson <seanga2 at gmail.com> wrote:
> >>>>>>
> >>>>>> On 1/27/22 10:05 AM, Simon Glass wrote:
> >>>>>>> Hi Sean,
> >>>>>>>
> >>>>>>> On Sat, 15 Jan 2022 at 15:25, Sean Anderson <seanga2 at gmail.com> wrote:
> >>>>>>>>
> >>>>>>>> When freeing a clock there is not much we can do if there is an error, and
> >>>>>>>> most callers do not actually check the return value. Even e.g. checking to
> >>>>>>>> make sure that clk->id is valid should have been done in request() in the
> >>>>>>>> first place (unless someone is messing with the driver behind our back).
> >>>>>>>> Just return void and don't bother returning an error.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
> >>>>>>>> ---
> >>>>>>>>
> >>>>>>>>      drivers/clk/clk-uclass.c  | 7 +++----
> >>>>>>>>      drivers/clk/clk_sandbox.c | 6 +++---
> >>>>>>>>      include/clk-uclass.h      | 8 +++-----
> >>>>>>>>      3 files changed, 9 insertions(+), 12 deletions(-)
> >>>>>>>>
> >>>>>>>
> >>>>>>> We have the same thing in other places too, but I am a little worried
> >>>>>>> about removing error checking. We try to avoid checking arguments too
> >>>>>>> much in U-Boot, due to code-size concerns, so I suppose I agree that
> >>>>>>> an invalid clk should be caught by a debug assertion rather than a
> >>>>>>> full check. But with driver model we have generally added an error
> >>>>>>> return to every uclass method, for consistency and to permit returning
> >>>>>>> error information if needed.
> >>>>>>>
> >>>>>>> Regards,
> >>>>>>> Simon
> >>>>>>>
> >>>>>>
> >>>>>> So there are a few reasons why I don't think a return value is useful
> >>>>>> here. To illustrate this, consider a typical user of the clock API:
> >>>>>>
> >>>>>>            struct clk a, b;
> >>>>>>
> >>>>>>            ret = clk_get_by_name(dev, "a", &a);
> >>>>>>            if (ret)
> >>>>>>                    return ret;
> >>>>>>
> >>>>>>            ret = clk_get_by_name(dev, "b", &b);
> >>>>>>            if (ret)
> >>>>>>                    goto free_a;
> >>>>>>
> >>>>>>            ret = clk_set_rate(&a, 5000000);
> >>>>>>            if (ret)
> >>>>>>                    goto free_b;
> >>>>>>
> >>>>>>            ret = clk_enable(&b);
> >>>>>>
> >>>>>> free_b:
> >>>>>>            clk_free(&b);
> >>>>>> free_a:
> >>>>>>            clk_free(&a);
> >>>>>>            return ret;
> >>>>>>
> >>>>>> - Because a and b are "thick pointers" they do not need any cleanup to
> >>>>>>       free their own resources. The only cleanup might be if the clock
> >>>>>>       driver has allocated something in clk_request (more on this below)
> >>>>>> - By the time we call clk_free, the mutable portions of the function
> >>>>>>       have already completed. In effect, the function has succeeded,
> >>>>>>       regardless of whether clk_free fails. Additionally, we cannot take any
> >>>>>>       action if it fails, since we still have to free both clocks.
> >>>>>> - clk_free occurs during the error path of the function. Even if it
> >>>>>>       errored, we do not want to override the existing error from one of the
> >>>>>>       functions doing "real" work.
> >>>>>>
> >>>>>> The last thing is that no clock driver actually does anything in rfree.
> >>>>>> The only driver with this function is the sandbox driver. I would like
> >>>>>> to remove the function altogether. As I understand it, the existing API
> >>>>>> is inspired by the reset drivers, so I would like to review its usage in
> >>>>>> the reset subsystem before removing it for the clock subsystem. I also
> >>>>>> want to make some changes to how rates and enables/disables are
> >>>>>> calculated which might provide a case for rfree. But once that is
> >>>>>> complete I think there will be no users still.
> >>>>>
> >>>>> What does this all look like in Linux?
> >>>>
> >>>> Their equivalent (clk_put) returns void, and generally so do most other
> >>>> cleanup functions, since .device_remove also returns void.
> >>>
> >>> We really cannot ignore errors from device_remove().
> >>
> >> Once you are at device_remove, all the users are gone and it's up to the
> >> device to clean up after itself. And often there is nothing we can do
> >> once remove is called. As you yourself say in device_remove,
> >>
> >>          /* We can't put the children back */
> >
> > Well this assumes that device_remove() is actually removing the
> > device, not just disabling DMA, etc.
> >
> >>
> >> Really the only sensible thing is to print an error and continue booting
> >> if possible.
> >>
> >> And of course no clock drivers actually use this function anyway, nor do
> >> (all but 5) users check it.
> >>
> >>> Anyway I think what you say about the 'thick pointer' makes sense. But
> >>> my expectation was that removing a clock might turn off a clock above
> >>> it in the tree, for example.
> >>
> >> No, this just frees resources (as is documented). If you want to turn
> >> off a clock, you have to call clk_disable. In fact, a very common use
> >> case is just like the example above, where the consmer frees the clock
> >> after enabling it.
> >>
> >> (This is also why clk->enable_count/rate are basically useless for
> >> anything other than CCF clocks)
> >
> > How about a clock provided by an audio codec on an I2C bus? Should
> > clk_free() do anything in that case? I assume not. I think the
> > compelling part of your argument is that it is a  'think pointer' and
> > disable does nothing. So can you update clk_rfree() etc. to document
> > what is allowed to be done in that function?
>
> The ideal case would be if you wanted to allocate some per-struct-clk
> data. Then, the correct place to free it would be rfree. But no one
> does this, and if they did it would probably be better to free things
> in remove.
>
> Actually... no one in clk, reset, or power-domain does anything with
> rfree. So I am inclined to just remove it altogether.

Well, I suppose it is easy enough to add later, if needed. What does
Linux use this for?


>
> --Sean
>
> > Reviewed-by: Simon Glass <sjg at chromium.org>
>

Regards,
SImon