Re: [PATCH v3 0/4] P2040/P2041 i2c recovery erratum
From: Joakim Tjernlund <hidden>
Date: 2021-05-12 08:57:45
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linux-i2c, linuxppc-dev, lkml
On Wed, 2021-05-12 at 01:48 +0000, Chris Packham wrote:
On 12/05/21 10:10 am, Joakim Tjernlund wrote:quoted
On Wed, 2021-05-12 at 09:20 +1200, Chris Packham wrote:quoted
The P2040/P2041 has an erratum where the i2c recovery scheme documented in the reference manual (and currently implemented in the i2c-mpc.c driver) does not work. The errata document provides an alternative that does work. This series implements that alternative and uses a property in the devicetree to decide when the alternative mechanism is needed. Chris Packham (4): dt-bindings: i2c: mpc: Add fsl,i2c-erratum-a004447 flag powerpc/fsl: set fsl,i2c-erratum-a004447 flag for P2041 i2c controllers powerpc/fsl: set fsl,i2c-erratum-a004447 flag for P1010 i2c controllers i2c: mpc: implement erratum A-004447 workaround .../devicetree/bindings/i2c/i2c-mpc.yaml | 7 ++ arch/powerpc/boot/dts/fsl/p1010si-post.dtsi | 8 ++ arch/powerpc/boot/dts/fsl/p2041si-post.dtsi | 16 ++++ drivers/i2c/busses/i2c-mpc.c | 81 ++++++++++++++++++- 4 files changed, 110 insertions(+), 2 deletions(-)This now reminds me about the current I2C reset procedure, it didn't work for us and I came up with this one: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Flinux-i2c%2Fmsg29490.html&data=04%7C01%7CJoakim.Tjernlund%40infinera.com%7Cb85a6e9c3c8b469572da08d914e816b5%7C285643de5f5b4b03a1530ae2dc8aaf77%7C1%7C0%7C637563809322419998%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=4cwujNmAVlBa08Tt79hLYGJfJtn7wdz1Kgz0eW2VX9U%3D&reserved=0 it never got in but we are still using it.For those reading along the v2 mentioned in that thread was posted as https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flinux-i2c%2F20170511122033.22471-1-joakim.tjernlund%40infinera.com%2F&data=04%7C01%7CJoakim.Tjernlund%40infinera.com%7Cb85a6e9c3c8b469572da08d914e816b5%7C285643de5f5b4b03a1530ae2dc8aaf77%7C1%7C0%7C637563809322419998%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=YDTX5L6J2ocHep5XutVN46jUpvJj7h1aDbHHwMqlrAs%3D&reserved=0 there was a bit of discussion but it seemed to die out without reaching a conclusion. The i2c-mpc driver is now using the generic recovery mechanism so that addresses one bit of feedback from the original thread. I do wonder if the reason the recovery wasn't working for your case was because of the erratum. Do you happen to remember which SoC your issue was on?
It could only be P2010 or MPC8321, I think it was MPC8321, you could try my solution on your CPU if you want to make sure.
I've been doing my recent work with a P2040 and prior to that I did test out the recovery on a T2081 (which isn't documented to have this erratum) when I was re-working the driver. The "new" recovery actually seems better but I don't have a reliably faulty i2c device so that's only based on me writing some code to manually trigger the recovery (using the snippet below) and observing it with an oscilloscope.
You don't need a faulty device, just an aborted I2C read/write op. You could force one such I2C op. by py pulling down the clock/SDA in the middle of a byte transfer. Jocke