Re: [PATCH v5 2/2] backlight: ktz8866: Add support for Kinetic KTZ8866 backlight

Jianhua Lu
2023-01-18T13:16:09Z

On Wed, Jan 18, 2023 at 12:08:01PM +0000, Daniel Thompson wrote:
> On Tue, Jan 17, 2023 at 11:44:08PM +0800, Jianhua Lu wrote:
> > Add support for Kinetic KTZ8866 backlight, which is used in
> > Xiaomi tablet, Mi Pad 5 series. This driver lightly based on
> > downstream implementation [1].
> > [1] https://github.com/MiCode/Xiaomi_Kernel_OpenSource/blob/elish-r-oss/drivers/video/backlight/ktz8866.c
> >
> > Signed-off-by: Jianhua Lu <lujianhua000@gmail.com>
> > ---
> > Changes in v2:
> > - Add missing staitc modifier to ktz8866_write function.
> >
> > Changes in v3:
> > - Add 2022 to Copyright line.
> > - Sort headers.
> > - Remove meaningless comment.
> > - Use definitions instead of hardcoding.
> > - Add missing maintainer info.
> >
> > Changes in v4:
> > - Change 2022 to 2023.
> > - Remove useless macro and enum.
> > - Describe settings by devicetree.
> > - Move header file to C file.
> > Changes in v5:
> > - Change "2023" to "2022, 2023" in Copyright line.
> > - Set scale property for backlight.
> >
> > MAINTAINERS | 6 +
> > drivers/video/backlight/Kconfig | 8 ++
> > drivers/video/backlight/Makefile | 1 +
> > drivers/video/backlight/ktz8866.c | 201 ++++++++++++++++++++++++++++++
> > 4 files changed, 216 insertions(+)
> > create mode 100644 drivers/video/backlight/ktz8866.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 42fc47c6edfd..2084e74e1b58 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -11674,6 +11674,12 @@ M: John Hawley <warthog9@eaglescrag.net>
> > S: Maintained
> > F: tools/testing/ktest
> >
> > +KTZ8866 BACKLIGHT DRIVER
> > +M: Jianhua Lu <lujianhua000@gmail.com>
> > +S: Maintained
> > +F: Documentation/devicetree/bindings/leds/backlight/kinetic,ktz8866.yaml
> > +F: drivers/video/backlight/ktz8866.c
> > +
> > L3MDEV
> > M: David Ahern <dsahern@kernel.org>
> > L: netdev@vger.kernel.org
> > diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> > index 936ba1e4d35e..2845fd7e33ad 100644
> > --- a/drivers/video/backlight/Kconfig
> > +++ b/drivers/video/backlight/Kconfig
> > @@ -190,6 +190,14 @@ config BACKLIGHT_KTD253
> > which is a 1-wire GPIO-controlled backlight found in some mobile
> > phones.
> >
> > +config BACKLIGHT_KTZ8866
> > + tristate "Backlight Driver for Kinetic KTZ8866"
> > + depends on I2C
> > + select REGMAP_I2C
> > + help
> > + Say Y to enabled the backlight driver for the Kinetic KTZ8866
> > + found in Xiaomi Mi Pad 5 series.
>
> s/enabled/enable/ (and sorry for spotting this one so late)
Get it.
>
>
> > +++ b/drivers/video/backlight/ktz8866.c
> > @@ -0,0 +1,201 @@
> > [...]
> > +static void ktz8866_init(struct ktz8866 *ktz)
> > +{
> > + unsigned int val;
> > +
> > + if(of_property_read_u32(ktz->client->dev.of_node, "current-num-sinks", &val))
> > + ktz8866_write(ktz, BL_EN, BIT(val) - 1);
> > + else
> > + /* Enable all 6 current sinks if the number of current sinks isn't specifed. */
> > + ktz8866_write(ktz, BL_EN, BIT(6) - 1);
> > +
> > + if(of_property_read_u32(ktz->client->dev.of_node, "current-ramping-time-us", &val)) {
> > + if(val <= 128) {
> > + ktz8866_write(ktz, BL_CFG2, BIT(7) | (ilog2(val) << 3) | PWM_HYST);
> > + } else {
> > + ktz8866_write(ktz, BL_CFG2, BIT(7) | ((5 + val / 64) << 3) | PWM_HYST);
> > + }
>
> This code is interpreting current-ramping-time-us as milliseconds rather
> than microseconds!
>
> I know I used microseconds in the example I proposed in the feedback for
> v4 DT bindings but "something like" means I am merely providing an
> example (mostly I was intending to show that the units should be
> included both in the property name *and* description).
>
> It is up to you whether you fix the mismatch by changing the DT bindings
> document to current-ramping-time-ms or change this code to accept
> values in microseconds.
This is my mistake, sorry.
>
>
> > + }
> > +
> > + if(of_property_read_u32(ktz->client->dev.of_node, "led-ramping-time-us", &val)) {
> > + unsigned int ramp_off_time = ilog2(val) + 1;
> > + unsigned int ramp_on_time = ramp_off_time << 4;
> > + ktz8866_write(ktz, BL_DIMMING, ramp_on_time | ramp_off_time);
> > + }
>
> Similarly, this code has not adopted the units specified in the
> bindings documentation.
>
> In this case 0 would map to 512us so if you decided to use milliseconds
> you will need to add comment in the description saying that 0 will map
> to 512us because the hardware cannot ramp faster than this!
Get it, thank you very much.
>
>
> Daniel.