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openwrt/target/linux/bcm27xx/patches-6.6/950-1192-dts-rp1-hobble-DMA-AXI-burst-lengths.patch
Álvaro Fernández Rojas 0171157d45 bcm27xx: update to latest RPi patches
The patches were generated from the RPi repo with the following command:
git format-patch v6.6.44..rpi-6.6.y

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
2024-08-06 18:38:00 +02:00

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1.4 KiB
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From 4c1a665b465fa0e9d3369a467fc563ec812a47ce Mon Sep 17 00:00:00 2001
From: Jonathan Bell <jonathan@raspberrypi.com>
Date: Fri, 19 Jul 2024 13:07:59 +0100
Subject: [PATCH 1192/1215] dts: rp1: hobble DMA AXI burst lengths
Channels 1-2 have a statically configured maximum MSIZE of 8, and
channels 3-8 have MSIZE set to 4. The DMAC "helpfully" silently
truncates bursts to the hardware supported maximum, so any FIFO read
operation with an oversized burst threshold will leave a residue of
threshold minus MSIZE rows.
As channel allocation is dynamic, this means every client needs to use a
maximum of 4 for burst length.
AXI AWLEN/ARLEN constraints aren't strictly related to MSIZE, except
that bursts won't be issued that are longer than MSIZE beats. Therefore,
it's a useful proxy to tell clients of the DMAC the hardware
limitations.
Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>
---
arch/arm64/boot/dts/broadcom/rp1.dtsi | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/boot/dts/broadcom/rp1.dtsi
+++ b/arch/arm64/boot/dts/broadcom/rp1.dtsi
@@ -1064,7 +1064,7 @@
snps,data-width = <4>; // (8 << 4) == 128 bits
snps,block-size = <0x40000 0x40000 0x40000 0x40000 0x40000 0x40000 0x40000 0x40000>;
snps,priority = <0 1 2 3 4 5 6 7>;
- snps,axi-max-burst-len = <8>;
+ snps,axi-max-burst-len = <4>;
status = "disabled";
};