mbox series

[0/4] PWM and keyboard backlight driver for ARM Macs

Message ID 20221028165215.43662-1-fnkl.kernel@gmail.com
Headers
Series PWM and keyboard backlight driver for ARM Macs |

Message

Sasha Finkelstein Oct. 28, 2022, 4:52 p.m. UTC 
  Hi,

This series adds support for the PWM controller present on ARM Macs and used
among other things for the keyboard backlight on those laptops.

The included device tree patch also hooks up the keyboard backlight using
the pwm-leds binding.

Best Regards.

Sasha Finkelstein (4):
 dt-bindings: pwm: Add Apple PWM controller
 pwm: Add Apple PWM controller
 arm64: dts: apple: t8103: Add PWM controller
 MAINTAINERS: Add entries for Apple PWM driver

 Documentation/devicetree/bindings/pwm/pwm-apple.yaml |  51 +++++++++++++
 MAINTAINERS                                          |   2 ++
 arch/arm64/boot/dts/apple/t8103-j293.dts             |  20 ++++++++
 arch/arm64/boot/dts/apple/t8103-j313.dts             |  20 ++++++++
 arch/arm64/boot/dts/apple/t8103.dtsi                 |   9 ++++
 drivers/pwm/Kconfig                                  |  12 ++++
 drivers/pwm/Makefile                                 |   1 +
 drivers/pwm/pwm-apple.c                              | 124 +++++++++++++++++++
 8 files changed, 239 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/pwm-apple.yaml
 create mode 100644 drivers/pwm/pwm-apple.c

Comments

Krzysztof Kozlowski Oct. 28, 2022, 5:54 p.m. UTC | #1 
On 28/10/2022 12:52, Sasha Finkelstein wrote:
> Adds the Apple PWM controller driver.
> 
> Signed-off-by: Sasha Finkelstein <fnkl.kernel@gmail.com>
> ---
>  drivers/pwm/Kconfig     |  12 ++++
>  drivers/pwm/Makefile    |   1 +
>  drivers/pwm/pwm-apple.c | 124 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 137 insertions(+)
>  create mode 100644 drivers/pwm/pwm-apple.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 60d13a949bc5..ec6acb368073 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -51,6 +51,18 @@ config PWM_AB8500
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-ab8500.
>  
> +config PWM_APPLE
> +	tristate "Apple SoC PWM support"
> +	depends on ARCH_APPLE || (COMPILE_TEST && 64BIT)

Why this code cannot be build on 32-bit?

> +	help
> +	  Generic PWM framework driver for PWM controller present on
> +	  Apple SoCs
> +

Best regards,
Krzysztof
Sasha Finkelstein Oct. 28, 2022, 6:51 p.m. UTC | #2 
On Fri, 28 Oct 2022 at 20:54, Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 28/10/2022 12:52, Sasha Finkelstein wrote:
> > +config PWM_APPLE
> > +     tristate "Apple SoC PWM support"
> > +     depends on ARCH_APPLE || (COMPILE_TEST && 64BIT)
>
> Why this code cannot be build on 32-bit?
It uses 64-bit divisions, which causes it to fail to build on 32-bit
mips. It should not be a
problem, since this hardware is only present on 64-bit SoCs.
Krzysztof Kozlowski Oct. 28, 2022, 7:49 p.m. UTC | #3 
On 28/10/2022 14:51, Sasha Finkelstein wrote:
> On Fri, 28 Oct 2022 at 20:54, Krzysztof Kozlowski
> <krzysztof.kozlowski@linaro.org> wrote:
>>
>> On 28/10/2022 12:52, Sasha Finkelstein wrote:
>>> +config PWM_APPLE
>>> +     tristate "Apple SoC PWM support"
>>> +     depends on ARCH_APPLE || (COMPILE_TEST && 64BIT)
>>
>> Why this code cannot be build on 32-bit?
> It uses 64-bit divisions, which causes it to fail to build on 32-bit
> mips. It should not be a
> problem, since this hardware is only present on 64-bit SoCs.

Does not matter, code should be portable and buildable on 32-bit. If it
does not build then your code is not correct.

You need to investigate the failure. Maybe using do_div would solve (or
other macros from div64.h)

Best regards,
Krzysztof
Hector Martin Oct. 29, 2022, 6:25 a.m. UTC | #4 
On 29/10/2022 04.49, Krzysztof Kozlowski wrote:
> On 28/10/2022 14:51, Sasha Finkelstein wrote:
>> On Fri, 28 Oct 2022 at 20:54, Krzysztof Kozlowski
>> <krzysztof.kozlowski@linaro.org> wrote:
>>>
>>> On 28/10/2022 12:52, Sasha Finkelstein wrote:
>>>> +config PWM_APPLE
>>>> +     tristate "Apple SoC PWM support"
>>>> +     depends on ARCH_APPLE || (COMPILE_TEST && 64BIT)
>>>
>>> Why this code cannot be build on 32-bit?
>> It uses 64-bit divisions, which causes it to fail to build on 32-bit
>> mips. It should not be a
>> problem, since this hardware is only present on 64-bit SoCs.
> 
> Does not matter, code should be portable and buildable on 32-bit. If it
> does not build then your code is not correct.

This statement does not apply in general. There are plenty of drivers
which cannot reasonably build for 32-bit, and make no sense because no
32-bit hardware exists that could use them. Examples include anything
that accesses 64-bit registers on 64-bit SoCs the normal way, and
further anything that touches CPU stuff like system registers.

In *this* case, if the only issue is some 64-bit math, then yes, it
should be made to build on 32-bit (especially since this is likely to
also work for older 32-bit Apple SoCs). But the (COMPILE_TEST && 64BIT)
pattern is definitely valid in other cases, and I've been adding it
lately to shut up the kernel test bot since it makes no sense to compile
test a whole pile of our drivers on 32-bit architectures - they
fundamentally can't compile without adding pointless hypothetical broken
fluff to the driver like split MMIO accesses (which often can't work on
real hardware), and it serves no purpose.


- Hector