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Tue, 27 Oct 2026 14:37:36 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-ThreadId: AOq_Oqeu6MIs Date: Tue, 27 Oct 2026 19:37:16 +0100 From: "Arnd Bergmann" To: "Florian Fainelli" , "Andy Shevchenko" Cc: "Greg Kroah-Hartman" , "Jiri Slaby" , "Joshua Rogers" , "Chris Mason" , "Josef Bacik" , "Tony Lindgren" , "Rafael Gago Castano" , =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= , "Peter Hurley" , "Heikki Krogerus" , "Crescent Hsieh" , "Frank Li" , "Sherry Sun" , "Sascha Hauer" , "Pengutronix Kernel Team" , "Fabio Estevam" , "Manivannan Sadhasivam" , "Olof Johansson" , =?UTF-8?Q?Andreas_F=C3=A4rber?= , "Krzysztof Kozlowski" , "Peter Griffin" , "Alim Akhtar" , "Robert Baldyga" , "Thomas Abraham" , "Kukjin Kim" , "Patrice Chotard" , "Srinivas Kandagatla" , "Maxime Coquelin" , "Alexandre Torgue" , "Andy Shevchenko" , "Vladimir Zapolskiy" , "Al Cooper" , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, stable , "Broadcom internal kernel review list" Message-Id: <4243bcc1-63a7-449b-ab8f-4eb901aec7ee@app.fastmail.com> In-Reply-To: <8ef10868-b203-4846-bc47-2d046805e1d3@broadcom.com> References: <20261027-tty-llm-v1-0-99b0202ae546@linuxfoundation.org> <20261027-tty-llm-v1-9-99b0202ae546@linuxfoundation.org> <993d16f4-c8e6-4896-adf4-f7f36d937152@broadcom.com> <8ef10868-b203-4846-bc47-2d046805e1d3@broadcom.com> Subject: Re: [PATCH 09/24] serial: 8250: 8250_bcm7271: fix DMA address truncation to 32 bits Content-Type: text/plain Content-Transfer-Encoding: 7bit On Tue, Oct 27, 2026, at 18:19, Florian Fainelli wrote: > On 10/27/26 10:14, Andy Shevchenko wrote: >> On Tue, Oct 27, 2026 at 09:41:17AM -0700, Florian Fainelli wrote: >> You never know this. The use of u64 is simple as that: it goes to HW as 64-bit >> value no matter what. Note, in the past we used to have a problematic use of >> dma_addr_t exactly due to its dependency on the data bus size when programming >> HW, and hence, based on my experience, I hardly recommend not to use dma_addr_t >> in this case, use plain fixed u64. > > It's not a hot path where optimizing for bus transactions would make > sense, so I guess it's fine to use u64 and have the two halves > programmed accordingly. I would suggest also setting a 64-bit dma mask in this case. The reason that the temporary 32-bit address was always fine is that dma_alloc_coherent() is limited to a 32-bit address by default. Arnd