linux-kernel - Re: CXL memory device not created correctly

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Date:   Wed, 31 May 2023 20:12:16 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>
CC:     Davidlohr Bueso <dave@...olabs.net>, LiuLele <liu.lele@...com>,
        <dave.jiang@...el.com>, <Jonathan.Cameron@...wei.com>,
        <alison.schofield@...el.com>, <bhelgaas@...gle.com>,
        <bwidawsk@...nel.org>, <dan.j.williams@...el.com>,
        <helgaas@...nel.org>, <linux-acpi@...r.kernel.org>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <rostedt@...dmis.org>,
        <vishal.l.verma@...el.com>
Subject: Re: CXL memory device not created correctly

Luis Chamberlain wrote:
> On Fri, May 19, 2023 at 08:20:44AM -0700, Ira Weiny wrote:
> > Davidlohr Bueso wrote:
> > > On Fri, 19 May 2023, LiuLele wrote:
> > > 
> > > >In my testing CXL device /sys/bus/cxl/devices/mem0  not created, and the get error messages :
> > > >
> > > >```
> > > >cxl_pci 0000:0d:00.0: Failed to get interrupt for event Info log
> > > >```
> > > >
> > > >My test environment is a qemu CXL emulator with qemu v8.0.0, Linux kernel v6.3.0.
> > > >While with kernel 5.9.13,  /sys/bus/cxl/devices/mem0  can be created.
> > > 
> > > Yes, this can be annoying and would argue the probe should not error out.
> > 
> > I had to double check.  Events are mandatory on devices.  On checking
> > again interrupt support is mandatory as well.  So that is why I errored
> > out here.
> 
> The failure essentially creates a user visible regression whereas
> booting an older kernel fixes it. It is not a friendly error message
> when testing kernels / upgrading / test environments. The only thing
> I can think of is if a new kconfig symbol is introduced so to make
> such cases a bit more clearer for now as things get settled.

Ah I see now.  This is a qemu without the event support.  :-/

> 
> Otherwise for testing this creates a few cycles of just noise. And I'd
> imagine even a few developer hours.

I don't think the kernel should be changed for following the spec.  But I
do sympathize with you.  I know Jonathan is working to get the event
support into qemu soon.  I've reviewed that series (the patches I did not
author) so I think it will land soon.

Can this be weathered until then?

Ira