From: Brian Masney <masneyb@onstation.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Stephen Boyd <sboyd@kernel.org>, Andy Gross <agross@kernel.org>,
David Brown <david.brown@linaro.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
MSM <linux-arm-msm@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RESEND] ARM: dts: qcom: msm8974-hammerhead: add device tree bindings for vibrator
Date: Wed, 29 May 2019 06:12:31 -0400 [thread overview]
Message-ID: <20190529101231.GA14540@basecamp> (raw)
In-Reply-To: <CACRpkdZxu1LfK11OHEx5L_4kyjMZ7qERpvDzFj5u3Pk2kD1qRA@mail.gmail.com>
On Wed, May 29, 2019 at 11:13:15AM +0200, Linus Walleij wrote:
> On Mon, May 20, 2019 at 4:21 PM Stephen Boyd <sboyd@kernel.org> wrote:
>
> > > + vibrator@fd8c3450 {
> > > + compatible = "qcom,msm8974-vibrator";
> > > + reg = <0xfd8c3450 0x400>;
> >
> > This is inside the multimedia clk controller. The resource reservation
> > mechanism should be complaining loudly here. Is the driver writing
> > directly into clk controller registers to adjust a duty cycle of the
> > camera's general purpose clk?
> >
> > Can you add support for duty cycle to the qcom clk driver's RCGs and
> > then write a generic clk duty cycle vibrator driver that adjusts the
> > duty cycle of the clk? That would be better than reaching into the clk
> > controller registers to do this.
>
> There is something ontological about this.
>
> A clock with variable duty cycle, isn't that by definition a PWM?
> I don't suppose it is normal for qcom clocks to be able to control
> their duty cycle, but rather default to 50/50 as we could expect?
>
> I would rather say that maybe the qcom drivers/clk/qcom/* file
> should be exporting a PWM from the linux side of things
> rather than a clock for this thingie, and adding #pwm-cells
> in the DT node for the clock controller, making it possible
> to obtain PWMs right out of it, if it is a single device node for
> the whole thing.
>
> Analogous to how we have GPIOs that are ortogonally interrupt
> providers I don't see any big problem in a clock controller
> being clock and PWM provider at the same time.
>
> There is code in drivers/clk/clk-pwm to use a pwm as a clock
> but that is kind of the reverse use case, if we implement PWMs
> directly in a clock controller driver then these can be turned into
> clocks using clk-pwm.c should it be needed, right?
>
> Part of me start to question whether clk and pwm should even
> be separate subsystems :/ they seem to solve an overlapping
> problem space.
My first revision of this vibrator driver used the Linux PWM framework
due to the variable duty cycle:
https://lore.kernel.org/lkml/20180926235112.25710-1-masneyb@onstation.org/
I used the pwm-vibra driver on the input side.
Brian
next prev parent reply other threads:[~2019-05-29 10:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-16 8:50 [PATCH RESEND] ARM: dts: qcom: msm8974-hammerhead: add device tree bindings for vibrator Brian Masney
2019-05-20 14:21 ` Stephen Boyd
2019-05-22 8:23 ` Brian Masney
2019-05-24 1:20 ` Stephen Boyd
2019-05-29 9:13 ` Linus Walleij
2019-05-29 10:12 ` Brian Masney [this message]
2019-05-31 10:51 ` Linus Walleij
2019-06-23 10:53 ` Brian Masney
2019-06-24 22:29 ` Linus Walleij
2019-06-25 0:54 ` Brian Masney
2019-06-27 23:49 ` Stephen Boyd
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