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

Geert Uytterhoeven
2015-12-10T12:30:22Z

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