linux-kernel - Re: [PATCH v1 1/2] leds: aw200xx: support for hw pattern controllers

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Message-ID: <20240125130049.GF74950@google.com>
Date: Thu, 25 Jan 2024 13:00:49 +0000
From: Lee Jones <lee@...nel.org>
To: Martin Kurbanov <mmkurbanov@...utedevices.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc: Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	kernel@...utedevices.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v1 1/2] leds: aw200xx: support for hw pattern controllers

Looping in Jacek (LEDS) and Greg (SYFS) for some knowledgable input.

On Fri, 12 Jan 2024, Martin Kurbanov wrote:
> On 21.12.2023 19:10, Lee Jones wrote:
> > On Thu, 07 Dec 2023, Martin Kurbanov wrote:
> > 
> >> This led-controller supports 3 pattern controllers for auto breathing or
> >> group dimming control. Each pattern controller can work in auto
> >> breathing or manual control mode. All breathing parameters including
> >> rising/falling slope, on/off time, repeat times, min/max brightness
> >> and so on are configurable.
> >>
> >> Signed-off-by: Martin Kurbanov <mmkurbanov@...utedevices.com>
> >> ---
> >>  .../testing/sysfs-class-led-driver-aw200xx    | 108 +++
> >>  Documentation/leds/leds-aw200xx.rst           | 274 ++++++++
> >>  drivers/leds/leds-aw200xx.c                   | 649 ++++++++++++++++++
> >>  3 files changed, 1031 insertions(+)
> >>  create mode 100644 Documentation/leds/leds-aw200xx.rst
> > 
> > This interface is bananas.  Exposing an entire register interface to
> > sysfs does not sit will with me at all.  When we add support to a sysfs
> > class, we usually require it to be generic and work across all devices.
> > Adding device specific interfaces is generally decried and to be
> > avoided.  Don't forget, once we commit something to sysfs, it becomes
> > ABI and we have to support it forever.
> > 
> > A far better approach would be to add support for this in userspace
> > instead  You can use the standard I2C character device API to achieve
> > the same result.  That way we don't have the same level of commitment
> > and is generally a much more flexible/future-proof.
> > 
> 
> I used sysfs similarly to other LED drivers (for example, leds-lm3533).
> Additionally, the controller has interrupts about the completion of the pattern,
> which is best to handle in the kernel. In the case of implementation in user
> mode, there may be synchronization problems, as the controller has several
> memory pages that can be switched by writing the page number to register 0xF0.

leds-lm3533 is a 12 year old legacy exception AND has less than half of
the sysfs exports proposed here.  What makes aw200xx so different it
needs to an incomparable interface to any other that we currently
support?

-- 
Lee Jones [李琼斯]