[linux-sunxi] Re: [PATCH 4/4] simplefb: add clock handling code

[Geert Uytterhoeven]

Hi Thierry,

On Mon, Sep 29, 2014 at 12:18 PM, Thierry Reding
<thierry.reding at gmail.com> wrote:
>> How is that less generic?
>
> It's more generic. That's the whole point.
>
> The difference is that with the solution I proposed we don't have to
> keep track of all the resources. We know that firmware has set them up
> and we know that a real driver will properly take them over at some
> point, so duplicating what the real driver does within the simplefb
> driver is just that, duplication. We don't allow duplication anywhere
> else in the kernel, why should simplefb be an exception?
>
>> You know that you are going to call that for regulator, reset, power
>> domains, just as you would have needed to with the proper API, unless
>> that with this kind of solution, you would have to modify *every*
>> framework that might interact with any resource involved in getting
>> simplefb running?
>
> We have to add handling for every kind of resource either way. Also if
> this evolves into a common pattern we can easily wrap it up in a single
> function call.

disable_all_power_management(), as this is not limited to clocks.

>> Plus, speaking more specifically about the clocks, that won't prevent
>> your clock to be shut down as a side effect of a later clk_disable
>> call from another driver.

> Furthermore isn't it a bug for a driver to call clk_disable() before a
> preceding clk_enable()? There are patches being worked on that will
> enable per-user clocks and as I understand it they will specifically
> disallow drivers to disable the hardware clock if other drivers are
> still keeping them on via their own referenc.

Calling clk_disable() preceding clk_enable() is a bug.

Calling clk_disable() after clk_enable() will disable the clock (and
its parents)
if the clock subsystem thinks there are no other users, which is what will
happen here.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds