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[2003:e4:1f4b:7100:f22f:74ff:fe1f:3a53]) by smtp.gmail.com with ESMTPSA id o6-20020a05600c378600b003fbb9339b29sm18397591wmr.42.2023.07.13.06.37.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Jul 2023 06:37:38 -0700 (PDT) Date: Thu, 13 Jul 2023 15:37:36 +0200 From: Thierry Reding To: Jason Gunthorpe Cc: Stanimir Varbanov , linux-tegra@vger.kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Krishna Reddy , Will Deacon , Robin Murphy , Joerg Roedel Subject: Re: [RFC PATCH] iommu: arm-smmu-nvidia: Add default domain type implementation op Message-ID: References: <20230710082252.9702-1-svarbanov@suse.de> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="K6L+rgi8a0xrphCK" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.10 (2023-03-25) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --K6L+rgi8a0xrphCK Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jul 10, 2023 at 03:40:28PM -0300, Jason Gunthorpe wrote: > On Mon, Jul 10, 2023 at 11:22:52AM +0300, Stanimir Varbanov wrote: > > Add def_domain_type implementation op and override default IOMMU > > domain Kconfig option (CONFIG_IOMMU_DEFAULT_PASSTHROUGH=3Dy), which > > could be enabled on some distros. The current quirk has been done > > for Tegra234 machine, because I found the issue on it. The issue > > itself appears on USB host controller which cannot be initialized > > without IOMMU translation. Something more, we proved that IOMMU > > translation is needed for display and GPU drivers as well. >=20 > Generically, if you find HW combinations where certain end points > cannot work with passthrough (which is really weird in the first > place) it should be narrowly quirked - not just an entire platform. >=20 > Also we don't really have a way to force non-passthrough, ARM32 > systems will always run in passthrough, for instance. Broadly the > kernel expects it to work. As I mentioned in my other, lengthy reply, passthrough is a very undesirable configuration on more recent Tegra (Tegra186 and later at least). Passthrough support (or more generally non-SMMU support) is in a sad state at the moment because we rarely ever test it. I don't think it can't be fixed, but it's going to take a bit of effort and is likely to regress again in the future if we don't keep testing it continuously. 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