Re: [PATCH 2/3] ARM: exynos5420: dt: add clock entries to watchdog node

[Tomasz Figa <t.figa@samsung.com>]

On Wednesday 24 of July 2013 15:31:43 Sachin Kamat wrote:
> Hi Tomasz,
> 
> On 24 July 2013 15:24, Tomasz Figa <t.figa@samsung.com> wrote:
> > Hi Sachin,
> > 
> > On Wednesday 24 of July 2013 15:18:26 Sachin Kamat wrote:
> >> Hi Leela,
> >> 
> >> On 24 July 2013 15:08, Leela Krishna Amudala <l.krishna@samsung.com>
> > 
> > wrote:
> >> > This patch adds clock entries to watchdog node for exynos5420
> >> > as per the common clock framework of exynos5420
> >> > 
> >> > Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
> >> > Reviewed-by: Doug Anderson <dianders@chromium.org>
> >> > Signed-off-by: Leela Krishna Amudala <l.krishna@samsung.com>
> >> > ---
> >> > 
> >> >  arch/arm/boot/dts/exynos5420.dtsi |    6 ++++++
> >> >  1 file changed, 6 insertions(+)
> >> > 
> >> > diff --git a/arch/arm/boot/dts/exynos5420.dtsi
> >> > b/arch/arm/boot/dts/exynos5420.dtsi index 8c54c4b..e1d2d20 100644
> >> > --- a/arch/arm/boot/dts/exynos5420.dtsi
> >> > +++ b/arch/arm/boot/dts/exynos5420.dtsi
> >> > @@ -145,4 +145,10 @@
> >> > 
> >> >                 clocks = <&clock 260>, <&clock 131>;
> >> >                 clock-names = "uart", "clk_uart_baud0";
> >> >         
> >> >         };
> >> > 
> >> > +
> >> > +       watchdog {
> >> > +               clocks = <&clock 316>;
> >> > +               clock-names = "watchdog";
> >> > +               status = "okay";
> >> 
> >> Generally you do "okay" in specific board dts files.
> > 
> > Not necessarily. The status property should be set to okay whenever the
> > device represented by such node can already work with given set of
> > information (properties).
> > 
> > Given the fact that watchdog driver does not require any board specific
> > information, it can be instantiated regardless of the board.
> 
> Yes you are right. But I was thinking of keeping this (enabling) as an
> option at the board level.
> We do this for some of the other IPs too where even though we have all
> the properties we keep them disabled.

Yes and this is wrong. Device tree is only a way to list all the hardware 
present on particular platform. You don't define which components are used 
or not depending on use case, but rather all the hardware that can be used 
on given board should be enabled on DT level.

To illustrate the problem please consider that in the end, a dtb file will 
be fused into board ROM (or at most flash memory) and passed to the kernel 
by the bootloader. If you disable some hardware on DT level even if it can 
be physically used on the board, there will be no way to reenable it, if 
some user wanted to use it, because that would require editing the fused 
dtb.

Best regards,
Tomasz