Re: [RFC PATCH 02/15] cxl/core/hdm: Bail on endpoint init fail

From: Adam Manzanares <a.manzanares@samsung.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Ben Widawsky <ben.widawsky@intel.com>,
	"linux-cxl@vger.kernel.org" <linux-cxl@vger.kernel.org>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	"patches@lists.linux.dev" <patches@lists.linux.dev>,
	Alison Schofield <alison.schofield@intel.com>,
	Ira Weiny <ira.weiny@intel.com>,
	"Jonathan Cameron" <Jonathan.Cameron@huawei.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	"mcgrof@kernel.org" <mcgrof@kernel.org>
Subject: Re: [RFC PATCH 02/15] cxl/core/hdm: Bail on endpoint init fail
Date: Mon, 18 Apr 2022 16:37:12 +0000	[thread overview]
Message-ID: <20220418163702.GA85141@bgt-140510-bm01> (raw)
In-Reply-To: <CAPcyv4hKGEy_0dMQWfJAVVsGu364NjfNeup7URb7ORUYLSZncw@mail.gmail.com>

On Wed, Apr 13, 2022 at 02:31:42PM -0700, Dan Williams wrote:
> On Wed, Apr 13, 2022 at 11:38 AM Ben Widawsky <ben.widawsky@intel.com> wrote:
> >
> > Endpoint decoder enumeration is the only way in which we can determine
> > Device Physical Address (DPA) -> Host Physical Address (HPA) mappings.
> > Information is obtained only when the register state can be read
> > sequentially. If when enumerating the decoders a failure occurs, all
> > other decoders must also fail since the decoders can no longer be
> > accurately managed (unless it's the last decoder in which case it can
> > still work).
> 
> I think this should be expanded to fail if any decoder fails to
> allocate anywhere in the topology otherwise it leaves a mess for
> future address translation code to work through cases where decoder
> information is missing.
> 
> The current approach is based around the current expectation that
> nothing is enumerating pre-existing regions, and nothing is performing
> address translation.

Does the qemu support currently allow testing of this patch? If so, it would 
be good to reference qemu configurations. Any other alternatives would be 
welcome as well. 

+Luis on cc.

> 
> >
> > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> > ---
> >  drivers/cxl/core/hdm.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> > index bfc8ee876278..c3c021b54079 100644
> > --- a/drivers/cxl/core/hdm.c
> > +++ b/drivers/cxl/core/hdm.c
> > @@ -255,6 +255,8 @@ int devm_cxl_enumerate_decoders(struct cxl_hdm *cxlhdm)
> >                                       cxlhdm->regs.hdm_decoder, i);
> >                 if (rc) {
> >                         put_device(&cxld->dev);
> > +                       if (is_endpoint_decoder(&cxld->dev))
> > +                               return rc;
> >                         failed++;
> >                         continue;
> >                 }
> > --
> > 2.35.1
> >
> 