From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 23AF320DD52; Thu, 28 Aug 2025 14:09:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756390150; cv=none; b=hqZXoLNoFUM+FqCLifDCGBt3jKtku/5MMI/NzgZmWtNsuEOdwnOspo8XAyeHGx5yPnZ1tjpGl7aBXvlgBZQyrjxICuJrjiRIELdZFi+YVGk1fceL5lmILOQ9qok2UoiM/DB/okqqkj5EqvdaJLg8iGTLDFVC3fJbeweLaRVv2wk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756390150; c=relaxed/simple; bh=9lBWETV5L/TU142h0CIOLyDQrqk/HobWCZgRjMj0yoo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=GMyLB5sg9Czf+NSPzBmyLUqO0IEFcmmntOs8ViT6wFH5QqTFiIjiC9aYeN4mnlSQ/1L3n/kukzSLcPB/BHxF/t417U0nUJ9IeUnEaaR4ZuxpPEDBuvMRqYGAgd8TWezWsvN/U9uOt0/CdmGA9JyutH5U2DEFm99wzfvhLBQjhxI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EDFA11688; Thu, 28 Aug 2025 07:08:58 -0700 (PDT) Received: from e133380.arm.com (e133380.arm.com [10.1.197.68]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BE0943F694; Thu, 28 Aug 2025 07:09:01 -0700 (PDT) Date: Thu, 28 Aug 2025 15:08:45 +0100 From: Dave Martin To: James Morse Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, devicetree@vger.kernel.org, D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , peternewman@google.com, dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Rex Nie , Koba Ko , Shanker Donthineni , fenghuay@nvidia.com, baisheng.gao@unisoc.com, Jonathan Cameron , Rob Herring , Rohit Mathew , Rafael Wysocki , Len Brown , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Krzysztof Kozlowski , Conor Dooley , Catalin Marinas , Will Deacon , Greg Kroah-Hartman , Danilo Krummrich Subject: Re: [PATCH 01/33] cacheinfo: Expose the code to generate a cache-id from a device_node Message-ID: References: <20250822153048.2287-1-james.morse@arm.com> <20250822153048.2287-2-james.morse@arm.com> <17675117-79ef-42e3-9c21-4bc46e73d6b1@arm.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <17675117-79ef-42e3-9c21-4bc46e73d6b1@arm.com> Hi James, On Wed, Aug 27, 2025 at 06:11:25PM +0100, James Morse wrote: > Hi Dave, > > On 27/08/2025 11:46, Dave Martin wrote: > > On Fri, Aug 22, 2025 at 03:29:42PM +0000, James Morse wrote: > >> The MPAM driver identifies caches by id for use with resctrl. It > >> needs to know the cache-id when probe-ing, but the value isn't set > >> in cacheinfo until device_initcall(). > >> > >> Expose the code that generates the cache-id. The parts of the MPAM > >> driver that run early can use this to set up the resctrl structures > >> before cacheinfo is ready in device_initcall(). > > > Why can't the MPAM driver just consume the precomputed cache-id > > information? > > Because it would need to wait until cacheinfo was ready, and it would still > need a way of getting the cache-id for caches where all the CPUs are offline. > > The resctrl glue code has a waitqueue to wait for device_initcall_sync(), but that is > asynchronous to driver probing, its triggered by the schedule_work() from the cpuhp > callbacks. This bit is about the driver's use, which just gets probed whenever the core > code feels like it. > > I toyed with always using cacheinfo for everything, and just waiting - but the MPAM driver > already has to parse the PPTT to find the information it needs on ACPI platforms, so the > wait would only happen on DT. > > It seemed simpler to grab what the value would be, instead of waiting (or probe defer) - > especially as this is also needed for caches where all the CPUs are offline. > > (I'll add the offline-cpus angle to the commit message) Ack > > Possible reasons are that the MPAM driver probes too early, > > yup, > > > or that it > > must parse the PPTT directly (which is true) and needs to label caches > > consistently with the way the kernel does it. > > It needs to match what will be exposed to user-space from cacheinfo. > This isn't about the PPTT, its the value that is generated for DT systems. Right -- confused myself there. From the point of view of this series, the usage scenario isn't clear at this point. > The driver has to know if its ACPI or DT to call the appropriate thing to get cache-ids > before cacheinfo is ready. I see. This might be worth stating in the commit message. > >> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c > >> index 613410705a47..f6289d142ba9 100644 > >> --- a/drivers/base/cacheinfo.c > >> +++ b/drivers/base/cacheinfo.c > >> @@ -207,11 +207,10 @@ static bool match_cache_node(struct device_node *cpu, > >> #define arch_compact_of_hwid(_x) (_x) > >> #endif > >> > >> -static void cache_of_set_id(struct cacheinfo *this_leaf, > >> - struct device_node *cache_node) > >> +unsigned long cache_of_calculate_id(struct device_node *cache_node) > >> { > >> struct device_node *cpu; > >> - u32 min_id = ~0; > >> + unsigned long min_id = ~0UL; > > > Why the change of type here? > > This is a hang over from Rob's approach of making the cache-id 64 bit. Ah, right. (I have assumed that 0xffffffff is never going to clash with a valid value.) > > This does mean that 0xffffffff can now be generated as a valid cache-id, > > but if that is necessary then this patch is also fixing a bug in the > > code -- but the commit message doesn't say anything about that. > > > > For a patch that is just exposing an internal result, it may be > > better to keep the original type. ~(u32)0 is already used as an > > exceptional value. > > Yup, I'll fix that. OK -- it works either way, of course, but this should make the patch a little less noisy. Cheers ---Dave