From: Rob Herring <robh@kernel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Wolfram Sang <wsa@kernel.org>,
Chris Packham <chris.packham@alliedtelesis.co.nz>,
krzysztof.kozlowski+dt@linaro.org, gregory.clement@bootlin.com,
andi.shyti@kernel.org, conor+dt@kernel.org,
linux-i2c@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, Abel Vesa <abel.vesa@linaro.org>
Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: mv64xxx: add bus-reset-gpios property
Date: Fri, 27 Oct 2023 14:22:36 -0500 [thread overview]
Message-ID: <20231027192236.GA2946793-robh@kernel.org> (raw)
In-Reply-To: <7bfa2f6c-3e99-49a6-9b5a-81398d4bce7e@linaro.org>
On Fri, Oct 27, 2023 at 01:25:56PM +0200, Krzysztof Kozlowski wrote:
> On 27/10/2023 11:09, Wolfram Sang wrote:
> > On Fri, Oct 27, 2023 at 04:31:03PM +1300, Chris Packham wrote:
> >> Add bus-reset-gpios and bus-reset-duration-us properties to the
> >> marvell,mv64xxx-i2c binding. These can be used to describe hardware
> >> where a common reset GPIO is connected to all downstream devices on and
> >> I2C bus. This reset will be asserted then released before the downstream
> >> devices on the bus are probed.
> >>
> >> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
> >> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> >
> > Krzysztof, are you fine with this change?
>
> Actually no. NAK.
>
> Not because of the naming, but because the new name triggered some new
> paths in my brain which brought the point - this is old problem of power
> sequencing of children.
>
> I believe this must be solved in more generic way. First - generic for
> all I2C devices. Second - generic also matching other buses/subsystems,
> which have similar problem. We did it for USB (onboard USB), MMC
> (unloved MMC power sequence) and now we are doing it for PCIe and few
> others (Cc: Abel)
Unlike the others I2C doesn't expect to access the bus/device before
devices probe, right?
> https://lpc.events/event/17/contributions/1507/
Oh, good!
> Current solution is heavily limited. What about regulators? What about
> buses having 2 reset lines (still the same bus)? What about sequence?
A more complicated case should be handled by the device's driver. If the
GPIO reset was not shared we'd be handling it there too. I think what's
needed is to solve the shared aspect. That's already done with reset
subsys, so I think making 'reset-gpios' handled by it too is the way
forward. That would handle the QCA WiFi/BT case I think.
I'm not sure waiting for that or something else to happen is worth
holding up this simple case. It's not the only case of a common reset
for a bus (MDIO).
Rob
next prev parent reply other threads:[~2023-10-27 19:22 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-27 3:31 [PATCH v5 0/2] i2c: mv64xxx: bus-reset-gpios Chris Packham
2023-10-27 3:31 ` [PATCH v5 1/2] dt-bindings: i2c: mv64xxx: add bus-reset-gpios property Chris Packham
2023-10-27 9:09 ` Wolfram Sang
2023-10-27 11:25 ` Krzysztof Kozlowski
2023-10-27 19:22 ` Rob Herring [this message]
2023-10-28 7:51 ` Krzysztof Kozlowski
2023-10-27 3:31 ` [PATCH v5 2/2] i2c: mv64xxx: add an optional " Chris Packham
2023-10-27 8:48 ` Andi Shyti
2023-10-27 11:27 ` Krzysztof Kozlowski
2023-10-27 11:37 ` Krzysztof Kozlowski
2023-10-27 12:55 ` Andi Shyti
2023-10-29 21:02 ` Chris Packham
2023-10-27 15:10 ` Mark Brown
2023-10-29 20:48 ` Chris Packham
2023-10-31 6:01 ` Krzysztof Kozlowski
2023-10-31 19:59 ` Chris Packham
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