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From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Mark Brown <broonie@kernel.org>,
	Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
	Martin Sperl <kernel@martin.sperl.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/5] spi: bcm2835: Fix controller unregister order
Date: Sat, 16 May 2020 12:40:22 +0300
Message-ID: <CAHp75VeOSgiprNoqs2Jn=ibNRspSWyGwpqFmJphHd3K7999mrw@mail.gmail.com> (raw)
In-Reply-To: <20200516065607.zrqwlh5ayoth37y4@wunner.de>

On Sat, May 16, 2020 at 9:56 AM Lukas Wunner <lukas@wunner.de> wrote:
>
> On Sat, May 16, 2020 at 12:33:00AM +0300, Andy Shevchenko wrote:
> > On Fri, May 15, 2020 at 7:45 PM Lukas Wunner <lukas@wunner.de> wrote:
> > > On Fri, May 15, 2020 at 05:29:03PM +0100, Mark Brown wrote:
> > > > On Fri, May 15, 2020 at 05:58:02PM +0200, Lukas Wunner wrote:
> > > > > Fix by using the non-devm variant spi_register_controller().  Note that
> > > > > the struct spi_controller as well as the driver-private data are not
> > > > > freed until after bcm2835_spi_remove() has finished, so accessing them
> > > > > is safe.
> > > >
> > > > Why not use managed allocations of clocks and DMA channels?  This is a
> > > > standard issue with the devm APIs, if you're using them you basically
> > > > need to use them for *everything* up to the point where you start using
> > > > them.
> > >
> > > There is no devm version of clk_prepare_enable(), dma_request_chan()
> > > and various other functions invoked on ->probe() by spi-bcm2835.c.
> > > So tearing down DMA channels, disabling clocks etc needs to happen
> > > in the ->remove() hook and consequently devm_spi_register_controller()
> > > cannot be used.
> >
> > There is devm_add_action_or_reset (IIRC the name). It does a trick.
>
> Interesting, thanks.
>
> However there are currently four actions performed by bcm2835_spi_remove():
>

>         bcm2835_debugfs_remove(bs);

This one shouldn't be counted. You can init it as the last op in
->probe() and that mustn't fail the probe.

>         /* Clear FIFOs, and disable the HW block */
>         bcm2835_wr(bs, BCM2835_SPI_CS,
>                    BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX)

This one I don't know.

>         clk_disable_unprepare(bs->clk);

This one traditionally done via devm_add_action_or_reset.

>         bcm2835_dma_release(ctlr, bs);

This one probably the one which needs to be addressed ideally in DMA
engine for all.

>
> So I think I'd have to add four functions to perform these devm actions,
> which would add a lot more code than just the single line added by my
> patch.  It also seems doubtful that the teardown code will still be easy
> to follow.  And small patches like the ones I've submitted lend themselves
> better to backporting to stable.
>
> Mark, please provide guidance as to which variant you'd prefer:
> Switching to the non-devm variant of spi_register_controller() as I've
> done here or adding devm calls for all the existing teardown steps.

All generic devm_* APIs have a release counterparts, you can
explicitly call them in order you want during ->remove(). So, I still
see a benefit of devm_*() even in such cases (makes ->probe() much
easier).

-- 
With Best Regards,
Andy Shevchenko

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15 15:58 [PATCH 0/5] Raspberry Pi SPI unbind fixes Lukas Wunner
2020-05-15 15:58 ` [PATCH 1/5] spi: Fix controller unregister order Lukas Wunner
2020-05-15 16:27   ` Mark Brown
2020-05-15 16:31     ` Lukas Wunner
2020-05-15 21:37       ` Andy Shevchenko
2020-05-16  6:45         ` Lukas Wunner
2020-05-16  9:45           ` Andy Shevchenko
2020-05-15 15:58 ` [PATCH 2/5] spi: bcm2835: " Lukas Wunner
2020-05-15 16:29   ` Mark Brown
2020-05-15 16:44     ` Lukas Wunner
2020-05-15 21:33       ` Andy Shevchenko
2020-05-16  6:56         ` Lukas Wunner
2020-05-16  9:40           ` Andy Shevchenko [this message]
2020-05-15 15:58 ` [PATCH 3/5] spi: bcm2835aux: " Lukas Wunner
2020-05-15 15:58 ` [PATCH 4/5] spi: bcm2835: Tear down DMA before turning off SPI controller Lukas Wunner
2020-05-15 15:58 ` [PATCH 5/5] spi: Document devm_spi_register_controller() gotcha Lukas Wunner
2020-05-15 16:30   ` Mark Brown
2020-05-20 17:17 ` [PATCH 0/5] Raspberry Pi SPI unbind fixes Mark Brown

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