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[35.247.103.198]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7349fe51432sm21196b3a.70.2025.02.26.13.36.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Feb 2025 13:36:40 -0800 (PST) Date: Wed, 26 Feb 2025 13:36:35 -0800 From: William McVicker To: Rob Herring Cc: Zijun Hu , Zijun Hu , Saravana Kannan , Maxime Ripard , Robin Murphy , Grant Likely , Marc Zyngier , Andreas Herrmann , Marek Szyprowski , Catalin Marinas , Mike Rapoport , Oreoluwa Babatunde , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v4 09/14] of: reserved-memory: Fix using wrong number of cells to get property 'alignment' Message-ID: References: <20250109-of_core_fix-v4-0-db8a72415b8c@quicinc.com> <20250109-of_core_fix-v4-9-db8a72415b8c@quicinc.com> <20250113232551.GB1983895-robh@kernel.org> <97ac58b1-e37c-4106-b32b-74e041d7db44@quicinc.com> <20250226194505.GA3407277-robh@kernel.org> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: > I thought downstream kept kernels and DTs in sync, so the dts could be > fixed? For Pixel the kernel and DT are in sync, but I'm not sure about other devices. The problem in general though is now everyone would need to do a special coordination when updating to the newer LTS version to make sure their kernel matches the new DT. On 02/26/2025, Rob Herring wrote: > On Wed, Feb 26, 2025 at 2:31 PM Zijun Hu wrote: > > > > On 2025/2/27 03:45, Rob Herring wrote: > > >> Right, I think it's already backported to the LTS kernels, but if it breaks any > > >> in-tree users then we'd have to revert it. I just like Rob's idea to instead > > >> change the spec for obvious reasons 🙂 > > > While if it is downstream, it doesn't exist, I'm reverting this for now. > > > > perhaps, it is better for us to slow down here. > > > > 1) This change does not break any upstream code. > > is there downstream code which is publicly visible and is broken by > > this change ? > > We don't know that unless you tested every dts file. We only know that > no one has reported an issue yet. > > Even if we did test everything, there are DT's that aren't in the > kernel tree. It's not like this downstream DT is using some > undocumented binding or questionable things. It's a standard binding. > > Every time this code is touched, it breaks. This is not even the only > breakage right now[1]. You can find the Pixel 6/7/8/9 device trees on android.googlesource.com. You can see for zuma based devices (Pixel 9 for example) they have this [1]: &reserved_memory { #address-cells = <2>; #size-cells = <1>; vstream: vstream { compatible = "shared-dma-pool"; reusable; size = <0x4800000>; alignment = <0x0 0x00010000>; alloc-ranges = <0x9 0x80000000 0x80000000>, <0x9 0x00000000 0x80000000>, <0x8 0x80000000 0x80000000>, <0x0 0x80000000 0x80000000>; }; I understand this code is downstream, but as a general principle we shouldn't break backwards compatibilty. Thanks, Will [1] https://android.googlesource.com/kernel/devices/google/zuma/+/refs/heads/android-gs-shusky-6.1-android16-dp/dts/gs101-dma-heap.dtsi#147 > > > 2) IMO, the spec may be right. > > The type of size is enough to express any alignment wanted. > > For several kernel allocators. type of 'alignment' should be the type > > of 'size', NOT the type of 'address' > > As I said previously, it can be argued either way. > > Rob > > [1] https://lore.kernel.org/all/20250226115044.zw44p5dxlhy5eoni@pengutronix.de/