Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 3 Mar 2021 19:26:00 +0100
From:   Thierry Reding <thierry.reding@gmail.com>
To:     Nicolin Chen <nicoleotsuka@gmail.com>
Cc:     joro@8bytes.org, will@kernel.org, guillaume.tucker@collabora.com,
        vdumpa@nvidia.com, jonathanh@nvidia.com, digetx@gmail.com,
        linux-tegra@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/tegra-smmu: Fix mc errors on tegra124-nyan
Message-ID: <YD/UuLSeVTLMh6HG@ulmo.localdomain>
References: <20210218220702.1962-1-nicoleotsuka@gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="4ou0ZJPXLgmnnIia"
Content-Disposition: inline
In-Reply-To: <20210218220702.1962-1-nicoleotsuka@gmail.com>
User-Agent: Mutt/2.0.5 (da5e3282) (2021-01-21)
Precedence: bulk


--4ou0ZJPXLgmnnIia
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Thu, Feb 18, 2021 at 02:07:02PM -0800, Nicolin Chen wrote:
> Commit 25938c73cd79 ("iommu/tegra-smmu: Rework tegra_smmu_probe_device()")
> removed certain hack in the tegra_smmu_probe() by relying on IOMMU core to
> of_xlate SMMU's SID per device, so as to get rid of tegra_smmu_find() and
> tegra_smmu_configure() that are typically done in the IOMMU core also.
>=20
> This approach works for both existing devices that have DT nodes and other
> devices (like PCI device) that don't exist in DT, on Tegra210 and Tegra3
> upon testing. However, Page Fault errors are reported on tegra124-Nyan:
>=20
>   tegra-mc 70019000.memory-controller: display0a: read @0xfe056b40:
> 	 EMEM address decode error (SMMU translation error [--S])
>   tegra-mc 70019000.memory-controller: display0a: read @0xfe056b40:
> 	 Page fault (SMMU translation error [--S])
>=20
> After debugging, I found that the mentioned commit changed some function
> callback sequence of tegra-smmu's, resulting in enabling SMMU for display
> client before display driver gets initialized. I couldn't reproduce exact
> same issue on Tegra210 as Tegra124 (arm-32) differs at arch-level code.
>=20
> Actually this Page Fault is a known issue, as on most of Tegra platforms,
> display gets enabled by the bootloader for the splash screen feature, so
> it keeps filling the framebuffer memory. A proper fix to this issue is to
> 1:1 linear map the framebuffer memory to IOVA space so the SMMU will have
> the same address as the physical address in its page table. Yet, Thierry
> has been working on the solution above for a year, and it hasn't merged.
>=20
> Therefore, let's partially revert the mentioned commit to fix the errors.
>=20
> The reason why we do a partial revert here is that we can still set priv
> in ->of_xlate() callback for PCI devices. Meanwhile, devices existing in
> DT, like display, will go through tegra_smmu_configure() at the stage of
> bus_set_iommu() when SMMU gets probed(), as what it did before we merged
> the mentioned commit.
>=20
> Once we have the linear map solution for framebuffer memory, this change
> can be cleaned away.
>=20
> [Big thank to Guillaume who reported and helped debugging/verification]
>=20
> Fixes: 25938c73cd79 ("iommu/tegra-smmu: Rework tegra_smmu_probe_device()")
> Reported-by: Guillaume Tucker <guillaume.tucker@collabora.com>
> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> ---
>=20
> Guillaume, would you please give a "Tested-by" to this change? Thanks!
>=20
>  drivers/iommu/tegra-smmu.c | 72 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 71 insertions(+), 1 deletion(-)

Acked-by: Thierry Reding <treding@nvidia.com>

--4ou0ZJPXLgmnnIia
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=66rd
-----END PGP SIGNATURE-----

--4ou0ZJPXLgmnnIia--