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([2001:8a0:d6cd:9000:86f4:4e71:9fc8:3183]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fd456a6d7sm9618856f8f.19.2026.07.31.13.34.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 31 Jul 2026 13:34:04 -0700 (PDT) Message-ID: <6d9b28ec-0905-4cb0-9a62-980c7fa69572@reactivated.net> Date: Fri, 31 Jul 2026 21:34:02 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/5] iommu: Add Broadcom BCM2712 IOMMU driver To: Krzysztof Kozlowski Cc: "Joerg Roedel (AMD)" , Will Deacon , Robin Murphy , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Florian Fainelli , Broadcom internal kernel review list , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, nick.hollinghurst@raspberrypi.com, Jason Gunthorpe References: <20260727-bcm2712-iommu-submit-v2-0-0247b5c03de8@reactivated.net> <20260727-bcm2712-iommu-submit-v2-4-0247b5c03de8@reactivated.net> <20260730-small-solid-spoonbill-8a8bbd@quoll> Content-Language: en-US From: Daniel Drake In-Reply-To: <20260730-small-solid-spoonbill-8a8bbd@quoll> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30/07/2026 08:00, Krzysztof Kozlowski wrote: > On Mon, Jul 27, 2026 at 09:43:59PM +0100, Daniel Drake wrote: >> +static int bcm2712_iommu_init_cache(struct bcm2712_iommu *mmu, >> + struct platform_device *pdev) >> +{ >> + struct device *dev = &pdev->dev; >> + struct platform_device *cache_pdev; >> + struct device_node *cache_np; >> + >> + cache_np = of_parse_phandle(dev->of_node, "brcm,iommu-cache", 0); >> + >> + /* Fall back on 'cache' property used in old/downstream firmware */ >> + if (!cache_np) >> + cache_np = of_parse_phandle(dev->of_node, "cache", 0); > > NAK. > > You cannot have undocumented ABI. I asked you to drop this at v1. Is there any approach I should consider here in order to support existing shipped firmware versions that use the 'cache' property, or should I simply break compatibility? While I was working on another issue recently there was a lean towards supporting existing/wrong DTs at the end of https://lore.kernel.org/all/878q898ulx.wl-maz@kernel.org/ but admittedly that case has some different parameters: it was incorrect DT values (not incorrect ABI) and also was more severe (breaks boot). In this case if the system were to boot without iommu support it is not the end of the world. Thanks, Daniel