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Tue, 8 Apr 2025 08:37:40 -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: T702257fbe5397c0b Date: Tue, 08 Apr 2025 14:37:07 +0200 From: "Arnd Bergmann" To: "Geert Uytterhoeven" , "Arnd Bergmann" Cc: "Bjorn Helgaas" , "Jeff Hugo" , "Carl Vanderlip" , "Oded Gabbay" , "Takashi Sakamoto" , "Maarten Lankhorst" , "Maxime Ripard" , "Thomas Zimmermann" , "Dave Airlie" , "Simona Vetter" , "Alex Deucher" , =?UTF-8?Q?Christian_K=C3=B6nig?= , "Dave Airlie" , "Jocelyn Falempe" , "Patrik Jakobsson" , "Xinliang Liu" , "Tian Tao" , "Xinwei Kong" , "Sumit Semwal" , "Yongqin Liu" , "John Stultz" , "Sui Jingfeng" , "Lyude Paul" , "Danilo Krummrich" , "Gerd Hoffmann" , "Zack Rusin" , "Broadcom internal kernel review list" , "Lucas De Marchi" , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , "Rodrigo Vivi" , "Andrew Lunn" , "David S . Miller" , "Eric Dumazet" , "Jakub Kicinski" , "Paolo Abeni" , "Saurav Kashyap" , "Javed Hasan" , GR-QLogic-Storage-Upstream@marvell.com, "James E . J . Bottomley" , "Martin K. Petersen" , "Nilesh Javali" , "Manish Rangankar" , "Alex Williamson" , "Geert Uytterhoeven" , "Javier Martinez Canillas" , "Jani Nikula" , "Mario Limonciello" , =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= , "Lijo Lazar" , "Niklas Schnelle" , "Dmitry Baryshkov" , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux1394-devel@lists.sourceforge.net, amd-gfx@lists.freedesktop.org, "nouveau@lists.freedesktop.org" , virtualization@lists.linux.dev, spice-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, Netdev , linux-pci@vger.kernel.org, linux-scsi@vger.kernel.org, kvm@vger.kernel.org, "Greg Ungerer" Message-Id: <9abf582c-ea8e-42ca-a6d5-34c1e1932f95@app.fastmail.com> In-Reply-To: References: <20250407104025.3421624-1-arnd@kernel.org> Subject: Re: [RFC] PCI: add CONFIG_MMU dependency Content-Type: text/plain Content-Transfer-Encoding: 7bit On Tue, Apr 8, 2025, at 12:22, Geert Uytterhoeven wrote: > On Mon, 7 Apr 2025 at 12:40, Arnd Bergmann wrote: > >> --- a/drivers/pci/Kconfig >> +++ b/drivers/pci/Kconfig >> @@ -21,6 +21,7 @@ config GENERIC_PCI_IOMAP >> menuconfig PCI >> bool "PCI support" >> depends on HAVE_PCI >> + depends on MMU >> help >> This option enables support for the PCI local bus, including >> support for PCI-X and the foundations for PCI Express support. > > While having an MMU is a hardware feature, I consider disabling MMU > support software configuration. So this change prevents people from > disabling MMU support on a system that has both a PCI bus and an MMU. > But other people may not agree, or care? I created this patch after Greg said that the coldfire-v4 chips that have an MMU are not really used without it any more, and I had accidentally only build tested a patch without CONFIG_MMU. On ARM, CONFIG_MMU can no longer be disabled on CPUs that have one, this was a side-effect of the ARCH_MULTIPLATFORM conversion. I just tried building an SH7751 kernel with MMU disabled but PCI enable. This produces build errors in several files, clearly nobody has tried this in a long time. I'm not entirely sure about xtensa, but it seems that PCI is only supported on the "virt" platform, which in turn cannot turn off MMU, even if there are other platforms that can build with out without MMU enabled. Arnd