linux-kernel - Re: [PATCH] cxl/mbox: Add debug messages for supported mailbox commands

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Date:   Thu, 26 Jan 2023 15:45:09 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Robert Richter <rrichter@....com>,
        Alison Schofield <alison.schofield@...el.com>
CC:     Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cxl/mbox: Add debug messages for supported mailbox
 commands

Robert Richter wrote:
> Hi Alison,
> 
> On 22.01.23 21:39:33, Alison Schofield wrote:
> > On Thu, Jan 19, 2023 at 02:04:50PM +0100, Robert Richter wrote:
> > > Only unsupported mailbox commands are reported in debug messages. A
> > > list of supported commands is useful too. Change debug messages to
> > > also report the opcodes of supported commands.
> > 
> > Hi Robert,
> > I wonder if you can get this info another way. When I try this 
> > loading cxl_test today, I get 99 new messages. Is this going to
> > create too much noise with debug kernels?
> 
> There are 26 commands supported by the driver, so I assume there are
> at least 4 cards in your system? To me the number of messages looks ok
> for a debug kernel. And, most kernels have dyndbg enabled allowing to
> enable only messages of interest? Esp. if card initialization fails
> there is no way to get this information from userland. The list of
> unsupported commands is of less use than the one for supported. That
> is the intention for the change.

The debug message looks ok to me, I will just note that there has been
consideration for exporting the enabled commands list via
CXL_MEM_QUERY_COMMANDS [1]. I wouldn't be opposed to someone enabling that
as well, just need to be clear with userspace that not all kernels will
populate that status.

[1]: http://lore.kernel.org/r/63b4ec4e37cc1_5178e2941d@dwillia2-xfh.jf.intel.com.notmuch