[PATCH v3 0/4] P2040/P2041 i2c recovery erratum
Joakim.Tjernlund at infinera.com
Wed May 12 18:57:38 AEST 2021
On Wed, 2021-05-12 at 01:48 +0000, Chris Packham wrote:
> On 12/05/21 10:10 am, Joakim Tjernlund wrote:
> > On Wed, 2021-05-12 at 09:20 +1200, Chris Packham wrote:
> > > 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
> 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.
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