From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Saravana Kannan <saravanak@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Kevin Hilman <khilman@kernel.org>,
Ulf Hansson <ulf.hansson@linaro.org>,
Len Brown <len.brown@intel.com>, Len Brown <lenb@kernel.org>,
Pavel Machek <pavel@ucw.cz>,
Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@kernel.org>, Rob Herring <robh+dt@kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
Marc Zyngier <maz@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM list <linux-pm@vger.kernel.org>,
linux-clk <linux-clk@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Android Kernel Team <kernel-team@android.com>,
Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH v4 0/8] Make fw_devlink=on more forgiving
Date: Tue, 16 Feb 2021 09:05:28 +0100 [thread overview]
Message-ID: <CAMuHMdVodauqBmLMxsfi0kQtAFT8ruJ36LJL9YuQgqwQNKwHHg@mail.gmail.com> (raw)
In-Reply-To: <CAGETcx_4FGa-rzLp6bjXbm4F4R6H2W78+nM_kN=XPz5hswzANA@mail.gmail.com>
Hi Saravana,
On Mon, Feb 15, 2021 at 10:27 PM Saravana Kannan <saravanak@google.com> wrote:
> On Mon, Feb 15, 2021 at 4:38 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Fri, Feb 12, 2021 at 4:00 AM Saravana Kannan <saravanak@google.com> wrote:
> > > On Thu, Feb 11, 2021 at 5:00 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > - I2C on R-Car Gen3 does not seem to use DMA, according to
> > > > /sys/kernel/debug/dmaengine/summary:
> > > >
> > > > -dma4chan0 | e66d8000.i2c:tx
> > > > -dma4chan1 | e66d8000.i2c:rx
> > > > -dma5chan0 | e6510000.i2c:tx
> > >
> > > I think I need more context on the problem before I can try to fix it.
> > > I'm also very unfamiliar with that file. With fw_devlink=permissive,
> > > I2C was using DMA? If so, the next step is to see if the I2C relative
> > > probe order with DMA is getting changed and if so, why.
> >
> > More detailed log:
> >
> > platform e66d8000.i2c: Linked as a consumer to e6150000.clock-controller
> > platform e66d8000.i2c: Linked as a sync state only consumer to e6055400.gpio
> >
> > Why is e66d8000.i2c not linked as a consumer to e6700000.dma-controller?
>
> Because fw_devlink.strict=1 is not set and dma/iommu is considered an
> "optional"/"driver decides" dependency.
Oh, I thought dma/iommu were considered mandatory initially,
but dropped as dependencies in the late boot process?
>
> > platform e6700000.dma-controller: Linked as a consumer to
> > e6150000.clock-controller
>
> Is this the only supplier of dma-controller?
No, e6180000.system-controller is also a supplier.
> > platform e66d8000.i2c: Added to deferred list
> > platform e6700000.dma-controller: Added to deferred list
> >
> > bus: 'platform': driver_probe_device: matched device
> > e6700000.dma-controller with driver rcar-dmac
> > bus: 'platform': really_probe: probing driver rcar-dmac with
> > device e6700000.dma-controller
> > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral
> >
> > bus: 'platform': driver_probe_device: matched device e66d8000.i2c
> > with driver i2c-rcar
> > bus: 'platform': really_probe: probing driver i2c-rcar with device
> > e66d8000.i2c
> >
> > I2C becomes available...
> >
> > i2c-rcar e66d8000.i2c: request_channel failed for tx (-517)
> > [...]
> >
> > but DMA is not available yet, so the driver falls back to PIO.
> >
> > driver: 'i2c-rcar': driver_bound: bound to device 'e66d8000.i2c'
> > bus: 'platform': really_probe: bound device e66d8000.i2c to driver i2c-rcar
> >
> > platform e6700000.dma-controller: Retrying from deferred list
> > bus: 'platform': driver_probe_device: matched device
> > e6700000.dma-controller with driver rcar-dmac
> > bus: 'platform': really_probe: probing driver rcar-dmac with
> > device e6700000.dma-controller
> > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral
> > platform e6700000.dma-controller: Added to deferred list
> > platform e6700000.dma-controller: Retrying from deferred list
> > bus: 'platform': driver_probe_device: matched device
> > e6700000.dma-controller with driver rcar-dmac
> > bus: 'platform': really_probe: probing driver rcar-dmac with
> > device e6700000.dma-controller
> > driver: 'rcar-dmac': driver_bound: bound to device 'e6700000.dma-controller'
> > bus: 'platform': really_probe: bound device
> > e6700000.dma-controller to driver rcar-dmac
> >
> > DMA becomes available.
> >
> > Here userspace is entered. /sys/kernel/debug/dmaengine/summary shows
> > that the I2C controllers do not have DMA channels allocated, as the
> > kernel has performed no more I2C transfers after DMA became available.
> >
> > Using i2cdetect shows that DMA is used, which is good:
> >
> > i2c-rcar e66d8000.i2c: got DMA channel for rx
> >
> > With permissive devlinks, the clock controller consumers are not added
> > to the deferred probing list, and probe order is slightly different.
> > The I2C controllers are still probed before the DMA controllers.
> > But DMA becomes available a bit earlier, before the probing of the last
> > I2C slave driver.
>
> This seems like a race? I'm guessing it's two different threads
> probing those two devices? And it just happens to work for
> "permissive" assuming the boot timing doesn't change?
>
> > Hence /sys/kernel/debug/dmaengine/summary shows that
> > some I2C transfers did use DMA.
> >
> > So the real issue is that e66d8000.i2c not linked as a consumer to
> > e6700000.dma-controller.
>
> That's because fw_devlink.strict=1 isn't set. If you need DMA to be
> treated as a mandatory supplier, you'll need to set the flag.
>
> Is fw_devlink=on really breaking anything here? It just seems like
> "permissive" got lucky with the timing and it could break at any point
> in the future. Thought?
I don't think there is a race. fw_devlinks calling driver_deferred_probe_add()
on all consumers has a big impact on probe order.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2021-02-16 8:06 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20210205222651eucas1p28ef87073dea33c1c5224c14aa203bec5@eucas1p2.samsung.com>
2021-02-05 22:26 ` [PATCH v4 0/8] Make fw_devlink=on more forgiving Saravana Kannan
2021-02-05 22:26 ` [PATCH v4 1/8] driver core: fw_devlink: Detect supplier devices that will never be added Saravana Kannan
2021-02-05 22:26 ` [PATCH v4 2/8] of: property: Don't add links to absent suppliers Saravana Kannan
2021-02-09 21:25 ` Rob Herring
2021-02-05 22:26 ` [PATCH v4 3/8] driver core: Add fw_devlink.strict kernel param Saravana Kannan
2021-02-05 22:26 ` [PATCH v4 4/8] of: property: Add fw_devlink support for optional properties Saravana Kannan
2021-02-09 21:33 ` Rob Herring
2021-02-09 21:54 ` Saravana Kannan
2021-02-10 8:25 ` Geert Uytterhoeven
2021-02-05 22:26 ` [PATCH v4 5/8] driver core: fw_devlink: Handle suppliers that don't use driver core Saravana Kannan
2021-02-05 22:26 ` [PATCH v4 6/8] irqdomain: Mark fwnodes when their irqdomain is added/removed Saravana Kannan
2021-02-05 22:26 ` [PATCH v4 7/8] PM: domains: Mark fwnodes when their powerdomain " Saravana Kannan
2021-02-05 22:26 ` [PATCH v4 8/8] clk: Mark fwnodes when their clock provider " Saravana Kannan
2021-02-08 15:38 ` Rob Herring
2021-02-08 23:34 ` Saravana Kannan
2021-02-10 11:44 ` [PATCH] clk: Mark fwnodes when their clock provider is added Tudor Ambarus
2021-02-10 11:44 ` Tudor Ambarus
2021-02-11 13:00 ` Greg KH
2021-02-13 0:37 ` Stephen Boyd
[not found] ` <CGME20210325133159eucas1p297b769beb681743fb32d362a86cc6e3e@eucas1p2.samsung.com>
2021-03-25 13:31 ` Marek Szyprowski
2021-03-25 15:47 ` Geert Uytterhoeven
2021-03-25 18:25 ` Nicolas Saenz Julienne
2021-03-26 18:13 ` Stephen Boyd
2021-03-26 18:29 ` Geert Uytterhoeven
[not found] ` <161705310317.3012082.15148238105608149214@swboyd.mtv.corp.google.com>
2021-03-29 23:28 ` Saravana Kannan
[not found] ` <161706920822.3012082.10047587064612237296@swboyd.mtv.corp.google.com>
2021-03-30 6:58 ` Geert Uytterhoeven
[not found] ` <161715734080.2260335.881350237641202575@swboyd.mtv.corp.google.com>
2021-03-31 7:05 ` Geert Uytterhoeven
[not found] ` <161721871083.2260335.2392646934517115770@swboyd.mtv.corp.google.com>
2021-04-05 11:04 ` Nicolas Saenz Julienne
2021-04-21 3:26 ` Guenter Roeck
2021-04-21 7:00 ` Saravana Kannan
2021-02-10 19:13 ` Saravana Kannan
2021-03-30 15:42 ` Guenter Roeck
2021-03-30 16:26 ` Saravana Kannan
[not found] ` <161317679292.1254594.15797939257637374295@swboyd.mtv.corp.google.com>
2021-02-14 21:15 ` [PATCH v4 8/8] clk: Mark fwnodes when their clock provider is added/removed Saravana Kannan
2021-02-06 2:45 ` [PATCH v4 0/8] Make fw_devlink=on more forgiving Saravana Kannan
2021-02-06 19:41 ` Geert Uytterhoeven
2021-02-06 20:47 ` Saravana Kannan
2021-02-08 8:40 ` Marek Szyprowski
2021-02-08 23:57 ` Saravana Kannan
2021-02-10 8:19 ` Tudor.Ambarus
2021-02-10 8:54 ` Saravana Kannan
2021-02-10 10:02 ` Tudor.Ambarus
2021-02-10 19:14 ` Saravana Kannan
2021-02-11 13:00 ` Geert Uytterhoeven
2021-02-11 13:05 ` Geert Uytterhoeven
2021-02-12 2:59 ` Saravana Kannan
2021-02-12 8:14 ` Geert Uytterhoeven
2021-02-12 20:57 ` Saravana Kannan
2021-02-15 12:38 ` Geert Uytterhoeven
2021-02-15 21:26 ` Saravana Kannan
2021-02-16 8:05 ` Geert Uytterhoeven [this message]
2021-02-16 18:48 ` Saravana Kannan
2021-02-16 20:31 ` Geert Uytterhoeven
2021-02-17 23:57 ` Saravana Kannan
2021-02-25 9:21 ` Geert Uytterhoeven
2021-02-15 15:16 ` Geert Uytterhoeven
2021-02-15 21:57 ` Saravana Kannan
2021-02-16 12:58 ` Geert Uytterhoeven
2021-02-15 11:19 ` Geert Uytterhoeven
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