Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get()

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Laurent,

On Thu, Nov 19, 2015 at 9:38 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> On Thursday 19 November 2015 19:38:46 Geert Uytterhoeven wrote:
>> Transfer clock cleanup handling to the core device management code.
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>> ---
>>  drivers/tty/serial/sh-sci.c | 8 +++-----
>>  1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
>> index cba51da604253db6..9442961a198378c7 100644
>> --- a/drivers/tty/serial/sh-sci.c
>> +++ b/drivers/tty/serial/sh-sci.c
>> @@ -2216,7 +2216,7 @@ static struct uart_ops sci_uart_ops = {
>>  static int sci_init_clocks(struct sci_port *sci_port, struct device *dev)
>>  {
>>       /* Get the SCI functional clock. It's called "fck" on ARM. */
>> -     sci_port->fclk = clk_get(dev, "fck");
>> +     sci_port->fclk = devm_clk_get(dev, "fck");
>
> Have you tested what happens if you unbind the device from the driver while
> userspace has the serial port open ?

Yes I have. And I didn't notice any user-visible behavioral differences.

There is a small ordering difference, though: with clk_get() and clk_put(), the
explicit clk_put() is done before removing the device from its PM Domain
(which involces another call to clk_put() on the module clock):

    device_release_driver
        __device_release_driver
            platform_drv_remove
                sci_remove
                    sci_cleanup_single
                        __clk_put
                genpd_dev_pm_detach
                    pm_genpd_remove_device
                        pm_clk_destroy
                            __pm_clk_remove
                                __clk_put

When using devm_clk_get(), the managed cleanup is done after the device has
been removed from its PM Domain:

    device_release_driver
        __device_release_driver
            platform_drv_remove
                genpd_dev_pm_detach
                    pm_genpd_remove_device
                        pm_clk_destroy
                            __pm_clk_remove
                                __clk_put
            release_nodes
                __clk_put

This shouldn't make a difference, and applies to all other drivers using
devm_*(), and devices that are part of a PM Domain.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@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