Re: [PATCH 1/2 v2] drm/i915: Allow parsing of variable size child device entries from VBT

[David Weinehall <david.weinehall@linux.intel.com>]

On Thu, Aug 06, 2015 at 02:59:10PM +0100, Michel Thierry wrote:
> On 8/5/2015 9:59 AM, Daniel Vetter wrote:
> >On Tue, Aug 04, 2015 at 04:55:52PM +0300, David Weinehall wrote:
> >>VBT version 196 increased the size of common_child_dev_config. The parser
> >>code assumed that the size of this structure would not change.
> >>
> >>The modified code now copies the amount needed based on the VBT version,
> >>and emits a debug message if the VBT version is unknown (too new);
> >>since the struct config block won't shrink in newer versions it should
> >>be harmless to copy the maximum known size in such cases, so that's
> >>what we do, but emitting the warning is probably sensible anyway.
> >>
> >>In the longer run it might make sense to modify the parser code to
> >>use a version/feature mapping, rather than hardcoding things like this,
> >>but for now the variants are fairly managable.
> >>
> >>v2: Stricter size checks
> >>
> >>Signed-off-by: David Weinehall <david.weinehall@linux.intel.com>
> >
> >Since Chris mentioned that this should fix a regression I applied it to
> >drm-intel-fixes.
> >-Daniel
> >
> >>---
> >>  drivers/gpu/drm/i915/intel_bios.c |   26 ++++++++++++++++++++++----
> >>  1 file changed, 22 insertions(+), 4 deletions(-)
> >>
> >>diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> >>index 2ff9eb00fdec..8a1f3e1fc598 100644
> >>--- a/drivers/gpu/drm/i915/intel_bios.c
> >>+++ b/drivers/gpu/drm/i915/intel_bios.c
> >>@@ -1015,15 +1015,33 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
> >>       const union child_device_config *p_child;
> >>       union child_device_config *child_dev_ptr;
> >>       int i, child_device_num, count;
> >>-     u16     block_size;
> >>+     u8 expected_size;
> >>+     u16 block_size;
> >>
> >>       p_defs = find_section(bdb, BDB_GENERAL_DEFINITIONS);
> >>       if (!p_defs) {
> >>               DRM_DEBUG_KMS("No general definition block is found, no devices defined.\n");
> >>               return;
> >>       }
> >>-     if (p_defs->child_dev_size < sizeof(*p_child)) {
> >>-             DRM_ERROR("General definiton block child device size is too small.\n");
> >>+     if (bdb->version < 195) {
> >>+             expected_size = 33;
> >>+     } else if (bdb->version == 195) {
> >>+             expected_size = 37;
> >>+     } else if (bdb->version <= 197) {
> >>+             expected_size = 38;
> >>+     } else {
> >>+             expected_size = 38;
> >>+             DRM_DEBUG_DRIVER("Expected child_device_config size for BDB version %u not known; assuming %u\n", expected_size);
> 
> Hi, the line above throws a warning because there are two '%u' but only one
> variable. Looks like bdb->version should be the 1st printed value.

Good catch, your analysis is indeed correct.

Daniel, will you do the fixup or should I submit a fixed version?


Kind regards, David
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