Re: BOG: commit 89c7cb1608ac3 ("of/device: Update dma_range_map only when dev has valid dma-ranges") seems to break Pinephone display or LCDC

From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To: "H. Nikolaus Schaller" <hns@goldelico.com>
Cc: Rob Herring <robh@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Yong Wu <yong.wu@mediatek.com>,
	Discussions about the Letux Kernel <letux-kernel@openphoenux.org>,
	Robin Murphy <robin.murphy@arm.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: BOG: commit 89c7cb1608ac3 ("of/device: Update dma_range_map only when dev has valid dma-ranges") seems to break Pinephone display or LCDC
Date: Tue, 2 Feb 2021 10:56:56 +0100	[thread overview]
Message-ID: <YBkh6IZfmzaLWYPp@aptenodytes> (raw)
In-Reply-To: <81FE44A3-38C8-4B78-BB77-C09B4FC80B0A@goldelico.com>

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Hi Nikolaus,

On Tue 02 Feb 21, 10:18, H. Nikolaus Schaller wrote:
> Hi,
> since v5.11-rc6 my Pinephone display shows some moiré pattern.
> 
> I did a bisect between v5.11-rc5 and v5.11-rc6 and it told me that
> the commit mentioned in the subject is the reason.
> 
> Reverting it makes the display work again and re-reverting fail again.
> 
> IMHO it seems as if the display DMA of the pinephone (allwinner suni-a54)
> got influenced and stopped to scan the framebuffer.
> 
> The only dma-ranges I could find are defined here:
> 
> 	arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> 
> 	dma-ranges = <0x00000000 0x40000000 0xc0000000>;
> 
> but I can't tell if they are "valid" or not.
> 
> Any insights are welcome. And please direct to the right people/mailing lists
> if they are missing.

This may not be strictly the same thing, but is this patch in your tree:
https://patchwork.kernel.org/project/linux-arm-kernel/patch/20210115175831.1184260-2-paul.kocialkowski@bootlin.com/

If not, it's worth a try to add it. If it is, it's worth doing a revert.

My understanding is like DE2 does not need a particular DMA range and has DRAM
starting at 0x40000000 (just like the CPU) but it will map DRAM in a loop
before and after this address.

I suspect the issue shows because the pinephone has 2 GiB RAM while for other
boards with < 2 GiB RAM, removing 0x40000000 to the DMA addresses still points
to the same location. So IMO the MBUS dma-ranges shouldn't apply to DE2.
I think this is already the case in dt, but the mbus driver may add it if you
don't have that patch.

I think I have a few A64 boards around, but probably not with 2 GiB RAM.
If adding the patch doesn't help, I'll try to make a few test.

Cheers!

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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