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[76.183.103.62]) by smtp.gmail.com with ESMTPSA id i3-20020a05683033e300b00684152e9ff2sm2950281otu.0.2023.02.23.08.10.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Feb 2023 08:10:24 -0800 (PST) Date: Thu, 23 Feb 2023 10:10:21 -0600 From: Nabeel M Mohamed To: Jonathan Cameron Cc: linux-cxl@vger.kernel.org, Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , linuxarm@huawei.com Subject: Re: [PATCH v2] cxl/pci: Set the device timestamp Message-ID: References: <20230130151327.32415-1-Jonathan.Cameron@huawei.com> <20230222162700.00006d0f@Huawei.com> <20230223150524.00002501@Huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230223150524.00002501@Huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On Thu, Feb 23, 2023 at 03:05:24PM +0000, Jonathan Cameron wrote: > On Wed, 22 Feb 2023 21:55:09 -0600 > Nabeel M Mohamed wrote: > > > On Wed, Feb 22, 2023 at 04:27:00PM +0000, Jonathan Cameron wrote: > > > On Wed, 22 Feb 2023 09:34:14 -0600 > > > Nabeel M Mohamed wrote: > > > > > > > On Mon, Jan 30, 2023 at 03:13:27PM +0000, Jonathan Cameron wrote: > > > > > CXL r3.0 section 8.2.9.4.2 "Set Timestamp" recommends that the host sets > > > > > the timestamp after every Conventional or CXL Reset to ensure accurate > > > > > timestamps. This should include on initial boot up. The time base that > > > > > is being set is used by a device for the poison list overflow timestamp > > > > > and all event timestamps. Note that the command is optional and if > > > > > not supported and the device cannot return accurate timestamps it will > > > > > fill the fields in with an appropriate marker (see the specification > > > > > description of each timestamp). > > > > > > > > > > Signed-off-by: Jonathan Cameron > > > > > > > > > > > > > Hi Jonathan, > > > > > > > > Could you please educate me on the reason for not supporting a > > > > "Get Timestamp" mailbox command at this time? > > > > > > > > A use-case that I can think of for having "Get Timestamp" in the UAPI > > > > is to enable userspace to better correlate the timestamp in the device > > > > logs with the wall time by querying the current timestamp on the device. > > > > This could be useful if there's some inaccuracy or skew in the device > > > > timestamp. > > > > > > > > Would that be a valid use-case or am I misunderstanding something here? > > > > > > > > I can see why "Set Timestamp" is a kernel-internal command but fail to > > > > see why "Get Timestamp" cannot be in the UAPI. > > > > > > > > Hi Nabeel, > > > > > > I'd be fine with a patch adding the support, it just didn't solve my > > > immediate problem so I didn't want to make this patch more complex. > > > > > > Jonathan > > > > Great, thanks for clarifying Jonathan! > > > > I'll be happy to post a patch which adds support for "Get Timestamp". > > > > Btw, this will be my first patch to the CXL driver. > > So, I'm wondering if there's any checklist listing the prerequisites > > for submitting a patch to the CXL driver - for instance, requirements > > on adding new tests for coverage, any existing CXL regression suites > > that the patch must pass, etc. > > > > Any pointers on the above would be greatly appreciated! > > As we are talking about a userspace exposed feature, support on the ndctl > /cxl tools should probably follow soon after the kernel side of things. > > Jonathan Noted, thanks!