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| Started by | Laurent Pinchart <laurent.pinchart@ideasonboard.com> |
|---|---|
| First post | 2015-12-14 02:40 +0100 |
| Last post | 2015-12-14 16:50 +0100 |
| Articles | 3 — 2 participants |
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Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-12-14 02:40 +0100
Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() Geert Uytterhoeven <geert@linux-m68k.org> - 2015-12-14 11:40 +0100
Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-12-14 16:50 +0100
| From | Laurent Pinchart <laurent.pinchart@ideasonboard.com> |
|---|---|
| Date | 2015-12-14 02:40 +0100 |
| Subject | Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() |
| Message-ID | <qFqhj-7JY-3@gated-at.bofh.it> |
Hi Geert,
On Thursday 10 December 2015 13:30:18 Geert Uytterhoeven wrote:
> On Thu, Nov 19, 2015 at 9:38 PM, Laurent Pinchart 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.
I was more concerned about the clk_disable_unprepare() calls. The function is
called through the uart pm handler which is called when closing the uart
(uart_close()). It's a bit difficult to follow the dynamic code paths as I'm
not very familiar with the framework, but I was concerned that the would end
up calling clk_disable_unprepare() on a clock for which we have no reference
anymore. What prevents clk_disable_unprepare() from being called in the close
path after the device has been unbound ? And what ensures that the clocks get
unprepared when unbinding the device if the port is held open by a userspace
process ?
--
Regards,
Laurent Pinchart
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| From | Geert Uytterhoeven <geert@linux-m68k.org> |
|---|---|
| Date | 2015-12-14 11:40 +0100 |
| Message-ID | <qFyHU-4U5-23@gated-at.bofh.it> |
| In reply to | #1290771 |
Hi Laurent,
On Sun, Dec 13, 2015 at 8:39 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> On Thursday 10 December 2015 13:30:18 Geert Uytterhoeven wrote:
>> On Thu, Nov 19, 2015 at 9:38 PM, Laurent Pinchart 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.
>
> I was more concerned about the clk_disable_unprepare() calls. The function is
> called through the uart pm handler which is called when closing the uart
> (uart_close()). It's a bit difficult to follow the dynamic code paths as I'm
> not very familiar with the framework, but I was concerned that the would end
> up calling clk_disable_unprepare() on a clock for which we have no reference
> anymore. What prevents clk_disable_unprepare() from being called in the close
> path after the device has been unbound ? And what ensures that the clocks get
> unprepared when unbinding the device if the port is held open by a userspace
> process ?
Both questions are answered by uart_hangup():
- uart_hangup() sets port->count to zero, hence uart_close() returns early
(second return statement), long before it would call the uart pm handler.
- uart_hangup() calls uart_change_pm(state, UART_PM_STATE_OFF);
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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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| From | Laurent Pinchart <laurent.pinchart@ideasonboard.com> |
|---|---|
| Date | 2015-12-14 16:50 +0100 |
| Message-ID | <qFDxU-83l-3@gated-at.bofh.it> |
| In reply to | #1291078 |
Hi Geert,
On Monday 14 December 2015 11:34:11 Geert Uytterhoeven wrote:
> On Sun, Dec 13, 2015 at 8:39 PM, Laurent Pinchart wrote:
> > On Thursday 10 December 2015 13:30:18 Geert Uytterhoeven wrote:
> >> On Thu, Nov 19, 2015 at 9:38 PM, Laurent Pinchart 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.
> >
> > I was more concerned about the clk_disable_unprepare() calls. The function
> > is called through the uart pm handler which is called when closing the
> > uart (uart_close()). It's a bit difficult to follow the dynamic code
> > paths as I'm not very familiar with the framework, but I was concerned
> > that the would end up calling clk_disable_unprepare() on a clock for
> > which we have no reference anymore. What prevents clk_disable_unprepare()
> > from being called in the close path after the device has been unbound ?
> > And what ensures that the clocks get unprepared when unbinding the device
> > if the port is held open by a userspace process ?
>
> Both questions are answered by uart_hangup():
> - uart_hangup() sets port->count to zero, hence uart_close() returns early
> (second return statement), long before it would call the uart pm handler.
> - uart_hangup() calls uart_change_pm(state, UART_PM_STATE_OFF);
Thank you for making me slightly wiser :-)
--
Regards,
Laurent Pinchart
--
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