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From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Marek Vasut <marek.vasut@gmail.com>
Cc: linux-pci@vger.kernel.org,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Wolfram Sang <wsa@the-dreams.de>,
	linux-renesas-soc@vger.kernel.org, robh@kernel.org,
	robin.murphy@arm.com
Subject: Re: [PATCH V3 2/3] PCI: rcar: Do not abort on too many inbound dma-ranges
Date: Wed, 16 Oct 2019 17:18:46 +0100
Message-ID: <20191016161846.GC7457@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <75fb3519-80eb-fec2-d3eb-cc1b884fef25@gmail.com>

[+RobH, Robin]

On Wed, Oct 16, 2019 at 05:29:50PM +0200, Marek Vasut wrote:

[...]

> >> The firmware provides all the ranges which are available and usable,
> >> that's the hardware description and that should be in the DT.
> > 
> > If the HW (given that those dma-ranges are declared for the PCI host
> > controller) can't be programmed to enable those DMA ranges - those
> > ranges are neither available nor usable, ergo DT is broken.
> 
> The hardware can be programmed to enable those DMA ranges, just not all
> of them at the same time.

Ok, we are down to DT bindings interpretation then.

> It's not the job of the bootloader to guess which ranges might the next
> stage like best.

By the time this series:

https://patchwork.ozlabs.org/user/todo/linux-pci/?series=132419

is merged, your policy will require the host controller driver to
remove the DMA ranges that could not be programmed in the inbound
address decoders from the dma_ranges list, otherwise things will
fall apart.

> >> The firmware cannot decide the policy for the next stage (Linux in
> >> this case) on which ranges are better to use for Linux and which are
> >> less good. Linux can then decide which ranges are best suited for it
> >> and ignore the other ones.
> > 
> > dma-ranges is a property that is used by other kernel subsystems eg
> > IOMMU other than the RCAR host controller driver. The policy, provided
> > there is one should be shared across them. You can't leave a PCI
> > host controller half-programmed and expect other subsystems (that
> > *expect* those ranges to be DMA'ble) to work.
> > 
> > I reiterate my point: if firmware is broken it is better to fail
> > the probe rather than limp on hoping that things will keep on
> > working.
> 
> But the firmware is not broken ?

See above, it depends on how the dma-ranges property is interpreted,
hopefully we can reach consensus in this thread, I won't merge a patch
that can backfire later unless we all agree that what it does is
correct.

Lorenzo

  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-09 17:57 [PATCH V3 1/3] PCI: rcar: Move the inbound index check marek.vasut
2019-08-09 17:57 ` [PATCH V3 2/3] PCI: rcar: Do not abort on too many inbound dma-ranges marek.vasut
2019-08-16 13:23   ` Simon Horman
2019-08-16 13:28     ` Marek Vasut
2019-08-16 13:38       ` Simon Horman
2019-08-16 17:41         ` Marek Vasut
2019-10-21 10:18       ` Andrew Murray
2019-10-26 18:03         ` Marek Vasut
2019-10-26 20:36           ` Andrew Murray
2019-10-26 21:06             ` Andrew Murray
2019-11-06 23:37             ` Marek Vasut
2019-11-07 14:19               ` Andrew Murray
2019-10-16 15:00   ` Lorenzo Pieralisi
2019-10-16 15:10     ` Marek Vasut
2019-10-16 15:26       ` Lorenzo Pieralisi
2019-10-16 15:29         ` Marek Vasut
2019-10-16 16:18           ` Lorenzo Pieralisi [this message]
2019-10-16 18:12             ` Rob Herring
2019-10-16 18:17               ` Marek Vasut
2019-10-16 20:25                 ` Rob Herring
2019-10-16 21:15                   ` Marek Vasut
2019-10-16 22:26                     ` Rob Herring
2019-10-16 22:33                       ` Marek Vasut
2019-10-17  7:06                         ` Geert Uytterhoeven
2019-10-17 10:55                           ` Marek Vasut
2019-10-17 13:06                             ` Robin Murphy
2019-10-17 14:00                               ` Marek Vasut
2019-10-17 14:36                                 ` Rob Herring
2019-10-17 15:01                                   ` Marek Vasut
2019-10-18  9:53                                     ` Lorenzo Pieralisi
2019-10-18 12:22                                       ` Marek Vasut
2019-10-18 12:53                                         ` Robin Murphy
2019-10-18 14:26                                           ` Marek Vasut
2019-10-18 15:44                                             ` Robin Murphy
2019-10-18 16:44                                               ` Marek Vasut
2019-10-18 17:35                                                 ` Robin Murphy
2019-10-18 18:44                                                   ` Marek Vasut
2019-10-21  8:32                                                     ` Geert Uytterhoeven
2019-10-18 10:06                         ` Andrew Murray
2019-10-18 10:17                           ` Geert Uytterhoeven
2019-10-18 11:40                             ` Andrew Murray
2019-08-09 17:57 ` [PATCH V3 3/3] PCI: rcar: Recalculate inbound range alignment for each controller entry marek.vasut
2019-10-21 10:39   ` Andrew Murray
2019-08-16 10:52 ` [PATCH V3 1/3] PCI: rcar: Move the inbound index check Lorenzo Pieralisi
2019-08-16 10:59   ` Marek Vasut
2019-08-16 11:10     ` Lorenzo Pieralisi
2019-10-15 20:14 ` Marek Vasut
2019-10-21 10:11 ` Andrew Murray

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