On Wednesday 24 of July 2013 16:52:43 Sylwester Nawrocki wrote:
> On 07/24/2013 04:09 PM, Tomasz Figa wrote:
> > On Wednesday 24 of July 2013 20:56:15 Kukjin Kim wrote:
> >> Sachin Kamat wrote:
> >>> On 24 July 2013 16:42, Tomasz Figa <t.figa@xxxxxxxxxxx> wrote:
> >>>> On Wednesday 24 of July 2013 15:31:43 Sachin Kamat wrote:
> >>>>> On 24 July 2013 15:24, Tomasz Figa <t.figa@xxxxxxxxxxx> wrote:
> >>>>>> On Wednesday 24 of July 2013 15:18:26 Sachin Kamat wrote:
> >>>>>>> On 24 July 2013 15:08, Leela Krishna Amudala
> >>>>>>> <l.krishna@xxxxxxxxxxx>
> >>>>>>
> >>>>>> 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@xxxxxxxxxxx>
> >>>>>>>> Reviewed-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> >>>>>>>> Signed-off-by: Leela Krishna Amudala <l.krishna@xxxxxxxxxxx>
> >>>>>>>> ---
> >>>>>>>>
> >>>>>>>> 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.
> >>>
> >>> This is contrary to the fact that we disable everything by default in
> >>> the top level dt files and only enable them as required in the board
> >>> dts files.
> >>>
> >>>> 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.
> >>>
> >>> I believe some h/w will be disabled in dt only if it should not be
> >>> used for whatever reason. If there is no reason then ofcourse they
> >>> would be enabled IMHO. Whatever be the case the choice of enabling or
> >>> disabling should be done at the leaf node (at board level). No?
> >>
> >> In my opinion, some IPs can be disabled according to the board
> >> manager.
> >> And if updated DTB is required due to kernel updating or whatever, DTB
> >> should be updated accordingly.
> >
> > No, not really. DTB should considered as immutable and modification of
> > which should be allowed only in special cases. Currently such huge
> > special case is that our DT bindings are still in development and so
> > device tree is likely to change, but we are getting towards
> > stabilizing them and so things should be done with correct
> > assumptions.
> >
> >> One more, actually we don't have no general way to fuse DTB in
> >> firmware
> >> when kernel is updated. So board manger who controls/decides what
> >> features should be supported on their board should consider the
> >> board's
> >> features and environments...
>
> I agree, device tree needs to be really stable and well standardized
> to even consider storing it in OTP memory. In most cases it's not a big
> deal to update the firmware and same applies to DTB. And disabling IP
> blocks that will never be used in a complex SoC, depending on how the
> SoC is wired up on the board, should be IMO nothing unusual.
Yes, the case of IPs that are not wired up on the board is obvious, but if
such IP can be used even if it's not wired (consider our FIMC as an
example, which can be used as a mem to mem device, even without any camera
sensors connected) then DTB should allow users to use it. Users should not
be restricted by DTB.
> I think this discussion is more on _where_ we disable devices - in dtsi
> or board dts files, rather than _if_ we disable some IP blocks in
> firmware.
Where we put the status = "okay" or "disabled" clause is a completely
different question. It is just a convention. I suggested using following
convention:
- a device should have status = "disabled" in top level instance of its
node, if it can't be used without extra data from lower levels, otherwise
no status should be set for it, which defaults to "okay",
- status should be overridden to "okay" in an instance of device node
which provides sufficient amount of data to make the device operational, at
least to some extent.
> > Again, device tree is not a way to specify use cases. It is a way to
> > list hardware available on the platform and its parameters. DTB should
> > be set up in a way enabling users to use any hardware available on
> > their machines, without the need to change DTB.
>
> I don't think there is a reason not to allow to have some functionality
> disabled by the firmware. Embedded systems are often highly specialized
> and may use only a subset of functionality an SoC provides. And the
> Application Processor SoCs are often loaded with so many features it is
> sensible to have all disabled by default and enable only what's needed
> in the board dts file.
If firmware can set up the unused hardware to defined, disabled (powered
down) state, then it's fine. But as we all know, state left after firmware is
rarely ideal and we need drivers even for unused hardware to put it into
some defined (powered down) state.
In addition, having the device enabled in device tree doesn't imply that
such device must be used. The same for binding a driver to such device.
Having the driver loaded should not have any negative effects if the
hardware is not used. If it does, then something is wrong with such driver.
> It's probably better to stick to one rule - either
> all devices have status property set to "disabled" by default in common
> dtsi files or all are enabled by default. Having a mixture of both is a
> bit messy IMHO.
Not really. This is a well defined rule. According to ePAPR Version 1.1
chapter 2.3.4:
The status property indicates the operational status of a device.
“okay”
Indicates the device is operational
“disabled”
Indicates that the device is not presently operational, but it might
become operational in the future (for example, something is not
plugged in, or switched off).
This is not about the device being used or not, but whether it is
operational and can be used. Where we define value of this property is just
our convention, but it should represent the real environment, not something
a manager decided.
> Besides, I believe it should be all considered individually for each
> chipset. IMHO there is not much point in enforcing general rule that
> everything what's possible but not necessarily sensible should be
> enabled.
Device Tree is all about general rules. This is not a board file where you
are free to define whatever kind of proprietary method to pass platform
specific data to your drivers. If we don't enforce some general rules we
will end up with a real mess of each platform (or even parts of the same
platforms) doing completely different things, stretching device tree
infrastructure just to fit their needs.
Best regards,
Tomasz
--
To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
