Messages in this thread | | | Date | Wed, 15 Feb 2023 17:32:58 +0100 | From | Robert Richter <> | Subject | Re: [PATCH] cxl/port: Disable decoder setup for endpoints in RCD mode |
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On 14.02.23 14:28:51, Dan Williams wrote: > Robert Richter wrote: > > Dan, > > > > On 09.02.23 09:07:18, Dan Williams wrote: > > > Robert Richter wrote: > > > > In RCD mode the HDM decoder capability is optional for endpoints and > > > > may not exist. The HDM range registers are used instead. Since the > > > > driver relies on the existence of an HDM decoder capability, its > > > > absence will cause the initialization of a memory card to fail. > > > > > > > > Moreover, the driver also tries to enable or reuse enabled memory > > > > ranges. In the worst case this may lead to a system hang due to > > > > disabling system memory that was previously provided and setup by > > > > system firmware. > > > > > > > > To solve the issues described, disable decoder setup for RCD endpoints > > > > and instead rely exclusively on system firmware to enable those memory > > > > ranges. Decoders are used by the kernel to setup and configure CXL > > > > memory regions, esp. to enable and disable them. Since Hot-plug is not > > > > supported for devices in RCD mode, the ability to disable that memory > > > > by the kernel using a decoder is not a necessarily requirement, > > > > decoders are not needed then. > > > > > > > > Fixes: 34e37b4c432c ("cxl/port: Enable HDM Capability after validating DVSEC Ranges") > > > > Signed-off-by: Robert Richter <rrichter@amd.com> > > > > > > Does Dave's series address this problem? > > > > > > https://lore.kernel.org/linux-cxl/167588394236.1155956.8466475582138210344.stgit@djiang5-mobl3.local/ > > > > > > ...that is arranging for the driver to carry-on in the absence of the > > > HDM Decoder Capability. > > > > it might only solve the missing hdm decoder capability. I need to take > > a closer look if that also solves a system hang I was debugging which > > is caused by clearing the memory disable bit in the hdm dvsec range > > register. So the best would be to use this patch now to fix decoder > > initialization in RCD mode and then have Dave's patches on top. I am > > going to test the series too. > > My concern with this patch is that it skips HDM decoder enumeration > entirely in RCD mode. The CXL cards I have seen are CXL 1.1+ and do > export the HDM decoder capability. > > The driver turns off mem_enable in a few scenarios, one of them indeed > looks buggy, but does not seem to be the one you addressed. The driver > should only disable mem if it was also the agent that enabled mem, but > looks like it does not always do that. > > Can you confirm if this fixes this issue?
I have tested the HDM decoder emulation series (v5) and it fixes the issue. Looking into the paricular change for that, I hope to get a condensed fix for stable.
Thanks,
-Robert
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