linux-kernel - Re: [PATCH V13 8/9] cxl/port: Retry reading CDAT on failure

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Date:   Thu, 14 Jul 2022 13:44:25 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        "Alison Schofield" <alison.schofield@...el.com>,
        Lukas Wunner <lukas@...ner.de>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V13 8/9] cxl/port: Retry reading CDAT on failure

Ira Weiny wrote:
> On Thu, Jul 14, 2022 at 01:05:47PM -0700, Ira wrote:
> > On Thu, Jul 14, 2022 at 09:27:04AM -0700, Dan Williams wrote:
> > > ira.weiny@ wrote:
> > > > From: Ira Weiny <ira.weiny@...el.com>
> > > > 
> > > > The CDAT read may fail for a number of reasons but mainly it is possible
> > > > to get different parts of a valid state.  The checksum in the CDAT table
> > > > protects against this.
> > > 
> > > I don't know what "different parts of a valid state" means.
> > 
> > This text is stale but given what I know about how other entities may be
> > issuing queries without the kernel knowledge I'm not 100% sure that the data
> > read back will always be valid.
> > 
> > Regardless, this has already caught a bug in QEMU.
> > 
> > So I'm inclined to leave this check in because the checksum is there and should
> > can be validated if only to detect broken hardware.
> > 
> > I can update the commit message to clarify this.
> 
> Oh wait I thought this was the 'is valid' patch.
> 
> I can remove the retries if that was all you were concerned about.
> 

I was concerned that this patch was trying to accommodate CDAT changes
while the retrieval is running which should be obviated by not allowing
set-partition while the CDAT retrieval is running. So I want to see
single-shot CDAT retrieval underneath set-partition protection.