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Wed, 9 Apr 2025 15:07:48 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: Tbf81c49526c64944 Date: Wed, 09 Apr 2025 21:07:17 +0200 From: "Arnd Bergmann" To: "Geert Uytterhoeven" , "Miguel Ojeda" Cc: "FUJITA Tomonori" , "Richard Weinberger" , "Anton Ivanov" , "Johannes Berg" , linux-um@lists.infradead.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, "Logan Gunthorpe" , "Stephen Bates" , "Danilo Krummrich" , "Dinh Nguyen" Message-Id: In-Reply-To: References: <20250409061129.136788-1-fujita.tomonori@gmail.com> Subject: Re: [PATCH v1] um: fix incompatible argument type in iounmap() Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Wed, Apr 9, 2025, at 19:07, Geert Uytterhoeven wrote: > > On Wed, 9 Apr 2025 at 16:48, Miguel Ojeda > wrote: >> On Wed, Apr 9, 2025 at 8:16=E2=80=AFAM FUJITA Tomonori >> wrote: >> > >> > Align iounmap() signature with other architectures. >> >> Most indeed have `volatile`, but nios2 and m68k don't -- Cc'ing them >> just in case. > > Indeed. Apparently the volatile keyword has not always been there... > Why does iounmap() need the volatile keyword? > Why does pci_iounmap() not have the volatile keyword? In the old days, a lot of drivers marked MMIO pointers as 'volatile void *' rather than 'void __iomem *', so iounmap() and the readl() family of accessors need to be compatible with that type to avoid a warning. By the time we introduced pci_iomap()/pci_iounmap(), this was no longer common, so they never needed it. In theory we could go through all the old drivers and also remove the 'volatile' markers from struct members that store __iomem pointers, but there is no practical benefit to that. Arnd