linux-kernel - Re: [PATCH v7 4/7] pwm: ntxec: Add driver for PWM function in Netronix EC

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Date:   Mon, 11 Jan 2021 13:53:56 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Heiko Stuebner <heiko.stuebner@...obroma-systems.com>,
        Stephan Gerhold <stephan@...hold.net>,
        Lubomir Rintel <lkundrak@...sk>,
        Mark Brown <broonie@...nel.org>, allen <allen.chen@....com.tw>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Josua Mayer <josua.mayer@....eu>,
        Andreas Kemnade <andreas@...nade.info>,
        Arnd Bergmann <arnd@...db.de>, Daniel Palmer <daniel@...f.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v7 4/7] pwm: ntxec: Add driver for PWM function in
 Netronix EC

On Sat, Jan 09, 2021 at 07:02:17PM +0100, Jonathan Neuschäfer wrote:
> The Netronix EC provides a PWM output which is used for the backlight
> on some ebook readers. This patches adds a driver for the PWM output.
> 
> The .get_state callback is not implemented, because the PWM state can't
> be read back from the hardware.
> 
> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@....net>
> ---
> v7:
> - no changes
> 
> v6:
> - https://lore.kernel.org/lkml/20201208011000.3060239-5-j.neuschaefer@gmx.net/
> - Move period / duty cycle setting code to a function
> - Rename pwmchip_to_priv to ntxec_pwm_from_chip
> - Set period and duty cycle only before enabling the output
> - Mention that duty=0, enable=1 is assumed not to happen
> - Interleave writes to the period and duty cycle registers, to minimize the
>   window of time that an inconsistent state is configured
> 
> v5:
> - https://lore.kernel.org/lkml/20201201011513.1627028-5-j.neuschaefer@gmx.net/
> - Avoid truncation of period and duty cycle to 32 bits
> - Make ntxec_pwm_ops const
> - Use regmap_multi_reg_write
> - Add comment about get_state to ntxec_pwm_ops
> - Add comments about non-atomicity of (period, duty cycle) update
> 
> v4:
> - https://lore.kernel.org/lkml/20201122222739.1455132-5-j.neuschaefer@gmx.net/
> - Document hardware/driver limitations
> - Only accept normal polarity
> - Fix a typo ("zone" -> "zero")
> - change MAX_PERIOD_NS to 0xffff * 125
> - Clamp period to the maximum rather than returning an error
> - Rename private struct pointer to priv
> - Rearrage control flow in _probe to save a few lines and a temporary variable
> - Add missing MODULE_ALIAS line
> - Spell out ODM
> 
> v3:
> - https://lore.kernel.org/lkml/20200924192455.2484005-5-j.neuschaefer@gmx.net/
> - Relicense as GPLv2 or later
> - Add email address to copyright line
> - Remove OF compatible string and don't include linux/of_device.h
> - Fix bogus ?: in return line
> - Don't use a comma after sentinels
> - Avoid ret |= ... pattern
> - Move 8-bit register conversion to ntxec.h
> 
> v2:
> - https://lore.kernel.org/lkml/20200905133230.1014581-6-j.neuschaefer@gmx.net/
> - Various grammar and style improvements, as suggested by Uwe Kleine-König,
>   Lee Jones, and Alexandre Belloni
> - Switch to regmap
> - Prefix registers with NTXEC_REG_
> - Add help text to the Kconfig option
> - Use the .apply callback instead of the old API
> - Add a #define for the time base (125ns)
> - Don't change device state in .probe; this avoids multiple problems
> - Rework division and overflow check logic to perform divisions in 32 bits
> - Avoid setting duty cycle to zero, to work around a hardware quirk
> ---
>  drivers/pwm/Kconfig     |   8 ++
>  drivers/pwm/Makefile    |   1 +
>  drivers/pwm/pwm-ntxec.c | 182 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 191 insertions(+)
>  create mode 100644 drivers/pwm/pwm-ntxec.c

Lee, I assume you'll want to pick the whole set up into the MFD tree? If
so:

Acked-by: Thierry Reding <thierry.reding@...il.com>

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