[PATCH v5 2/12] drm/ast: Handle configuration without P2A bridge
joel at jms.id.au
Fri Feb 24 13:43:47 AEDT 2017
On Fri, Feb 24, 2017 at 1:11 PM, Benjamin Herrenschmidt
<benh at kernel.crashing.org> wrote:
> The ast driver configures a window to enable access into BMC
> memory space in order to read some configuration registers.
> If this window is disabled, which it can be from the BMC side,
> the ast driver can't function.
> Closing this window is a necessity for security if a machine's
> host side and BMC side are controlled by different parties;
> i.e. a cloud provider offering machines "bare metal".
> A recent patch went in to try to check if that window is open
> but it does so by trying to access the registers in question
> and testing if the result is 0xffffffff.
> This method will trigger a PCIe error when the window is closed
> which on some systems will be fatal (it will trigger an EEH
> for example on POWER which will take out the device).
> This patch improves this in two ways:
> - First, if the firmware has put properties in the device-tree
> containing the relevant configuration information, we use these.
> - Otherwise, a bit in one of the SCU scratch registers (which
> are readable via the VGA register space and writeable by the BMC)
> will indicate if the BMC has closed the window. This bit has been
> defined by Y.C Chen from Aspeed.
> If the window is closed and the configuration isn't available from
> the device-tree, some sane defaults are used. Those defaults are
> hopefully sufficient for standard video modes used on a server.
> Signed-off-by: Russell Currey <ruscur at russell.cc>
> Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> v2. [BenH]
> - Reworked on top of Aspeed P2A patch
> - Cleanup overall detection via a "config_mode" and log the
> selected mode for diagnostics purposes
> - Add a property for the SCU straps
> v3. [BenH]
> - Moved the config mode detection to a separate functionn
> - Add reading of SCU 0x40 D to detect the window is
> closed as to not trigger a bus error by just "trying".
> (change provided by Y.C. Chen)
> v4. [BenH]
> - Only devices with the AST2000 PCI ID have a P2A bridge
> - Update the P2A presence test to account for VGA only
> mode as provided by Y.C. Chen.
> v5. [BenH]
> - Fixup prefix of OF properties based on Joel Stanley
> review comments.
LGTM. Thanks for the explaining the mcr regs, that stuff checks out now.
Acked-by: Joel Stanley <joel at jms.id.au>
> drivers/gpu/drm/ast/ast_drv.h | 6 +-
> drivers/gpu/drm/ast/ast_main.c | 264 +++++++++++++++++++++++++----------------
> drivers/gpu/drm/ast/ast_post.c | 7 +-
> 3 files changed, 168 insertions(+), 109 deletions(-)
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