From: Ben Wolsieffer <ben.wolsieffer@hefring.com>
To: Mark Brown <broonie@kernel.org>
Cc: linux-spi@vger.kernel.org,
linux-stm32@st-md-mailman.stormreply.com,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Alexandre Torgue <alexandre.torgue@foss.st.com>,
Alain Volmat <alain.volmat@foss.st.com>
Subject: Re: [PATCH] spi: stm32: enable controller before asserting CS
Date: Mon, 4 Dec 2023 14:54:00 -0500 [thread overview]
Message-ID: <ZW4uWBpEc2_4JR2b@dell-precision-5540> (raw)
In-Reply-To: <9aa5e049-bd1c-41a6-b9b8-037ebb4f54b8@sirena.org.uk>
On Mon, Dec 04, 2023 at 12:43:42PM +0000, Mark Brown wrote:
> On Fri, Dec 01, 2023 at 06:11:36PM -0500, Ben Wolsieffer wrote:
> > On Fri, Dec 01, 2023 at 09:50:33PM +0000, Mark Brown wrote:
> > > On Fri, Dec 01, 2023 at 04:40:14PM -0500, Ben Wolsieffer wrote:
>
> > > This feels like it'd be a good fit for moving to runtime PM - that way
> > > we avoid bouncing the controller on and off between messages which is
> > > probably better anyway. The driver already does pinctrl management for
> > > the device there.
>
> > Yes, that probably makes sense. There are a few bits that can only be
> > configured while the controller is disabled, but it doesn't look like
> > that applies to any of the ones set in stm32_spi_prepare_msg().
>
> > I'm a little hesitant to make big changes to the driver since I can only
> > test them on an STM32F7 though.
>
> It doesn't seem much more complex than what you're already proposing.
I'm working on a new patch that uses runtime PM and will submit it soon.
> > > It also occurs to me that this isn't going to work for devices which
> > > chip select inverted - for them we can't stop driving chip select at all
> > > since they need it held high when idle. There aren't that many such
> > > devices and it'd loose us the PM which is rather awkward... I guess
> > > that's an incremental issue with a more invasive fix though.
>
> > The driver only supports GPIO chip select rather than native, so I don't
> > think this is a problem. Also, I don't think there's any difference
>
> So mentioning the drive seems a bit confusing then?
Yes, I should have been more specific in the patch that only MOSI and
CLK float when the controller is disabled and that CS remains driven.
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prev parent reply other threads:[~2023-12-04 19:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-01 21:40 [PATCH] spi: stm32: enable controller before asserting CS Ben Wolsieffer
2023-12-01 21:50 ` Mark Brown
2023-12-01 23:11 ` Ben Wolsieffer
2023-12-04 12:43 ` Mark Brown
2023-12-04 19:54 ` Ben Wolsieffer [this message]
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