From: Marek Vasut <marek.vasut@gmail.com>
To: Robin Murphy <robin.murphy@arm.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Rob Herring <robh@kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
PCI <linux-pci@vger.kernel.org>,
Geert Uytterhoeven <geert+renesas@glider.be>,
Wolfram Sang <wsa@the-dreams.de>,
"open list:MEDIA DRIVERS FOR RENESAS - FCP"
<linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH V3 2/3] PCI: rcar: Do not abort on too many inbound dma-ranges
Date: Fri, 18 Oct 2019 16:26:29 +0200 [thread overview]
Message-ID: <3f2f3868-676c-edc4-0de1-d42b63186128@gmail.com> (raw)
In-Reply-To: <ce7d16ab-31b8-0992-b1d7-24f4a652ce5f@arm.com>
On 10/18/19 2:53 PM, Robin Murphy wrote:
> On 18/10/2019 13:22, Marek Vasut wrote:
>> On 10/18/19 11:53 AM, Lorenzo Pieralisi wrote:
>>> On Thu, Oct 17, 2019 at 05:01:26PM +0200, Marek Vasut wrote:
>>>
>>> [...]
>>>
>>>>> Again, just handling the first N dma-ranges entries and ignoring the
>>>>> rest is not 'configure the controller correctly'.
>>>>
>>>> It's the best effort thing to do. It's well possible the next
>>>> generation
>>>> of the controller will have more windows, so could accommodate the
>>>> whole
>>>> list of ranges.
>
> In the context of DT describing the platform that doesn't make any
> sense. It's like saying it's fine for U-Boot to also describe a bunch of
> non-existent CPUs just because future SoCs might have them. Just because
> the system would probably still boot doesn't mean it's right.
It's the exact opposite of what you just described -- the last release
of U-Boot currently populates a subset of the DMA ranges, not a
superset. The dma-ranges in the Linux DT currently are a superset of
available DRAM on the platform.
>>>> Thinking about this further, this patch should be OK either way, if
>>>> there is a DT which defines more DMA ranges than the controller can
>>>> handle, handling some is better than failing outright -- a PCI which
>>>> works with a subset of memory is better than PCI that does not work
>>>> at all.
>>>
>>> OK to sum it up, this patch is there to deal with u-boot adding multiple
>>> dma-ranges to DT.
>>
>> Yes, this patch was posted over two months ago, about the same time this
>> functionality was posted for inclusion in U-Boot. It made it into recent
>> U-Boot release, but there was no feedback on the Linux patch until
>> recently.
>>
>> U-Boot can be changed for the next release, assuming we agree on how it
>> should behave.
>>
>>> I still do not understand the benefit given that for
>>> DMA masks they are useless as Rob pointed out and ditto for inbound
>>> windows programming (given that AFAICS the PCI controller filters out
>>> any transaction that does not fall within its inbound windows by default
>>> so adding dma-ranges has the net effect of widening the DMA'able address
>>> space rather than limiting it).
>>>
>>> In short, what's the benefit of adding more dma-ranges regions to the
>>> DT (and consequently handling them in the kernel) ?
>>
>> The benefit is programming the controller inbound windows correctly.
>> But if there is a better way to do that, I am open to implement that.
>> Are there any suggestions / examples of that ?
>
> The crucial thing is that once we improve the existing "dma-ranges"
> handling in the DMA layer such that it *does* consider multiple entries
> properly, platforms presenting ranges which don't actually exist will
> almost certainly start going wrong, and are either going to have to fix
> their broken bootloaders or try to make a case for platform-specific
> workarounds in core code.
Again, this is exactly the other way around, the dma-ranges populated by
U-Boot cover only existing DRAM. The single dma-range in Linux DT covers
even the holes without existing DRAM.
So even if the Linux dma-ranges handling changes, there should be no
problem.
[...]
--
Best regards,
Marek Vasut
next prev parent reply other threads:[~2019-10-18 14:26 UTC|newest]
Thread overview: 52+ 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
2019-11-16 15:48 ` Marek Vasut
2019-11-18 18:42 ` Robin Murphy
2019-12-22 7:46 ` Marek Vasut
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
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 [this message]
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
2019-11-19 12:10 ` Robin Murphy
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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