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

[Simon Glass]

HI Sean,

On Wed, 16 Mar 2022 at 10:18, Sean Anderson <seanga2 at gmail.com> wrote:
>
> On 3/1/22 9:58 AM, Simon Glass wrote:
> > 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?
>
> As far as I can tell, Linux doesn't have request/free. There's
> of_clk_provider->get(), but that corresponds more to of_xlate.
> Similarly, there's reset_controller_dev->of_xlate(), but no request/free.

OK, sounds good then.

Regards,
Simon