On Tue, Jul 28, 2026 at 04:17:14PM +0100, Liviu Dudau wrote: > On Mon, Jul 20, 2026 at 03:55:18PM +0200, Osama Abdelkader wrote: > > The firmware exposes the global group count and per-group stream count in > > the shared control interface. These values are validated before being used > > as loop bounds, but the memory is shared with the MCU firmware and can be > > changed after validation. > > Again, you're making statements that need to be proven here. How is MCU > firmware going to change the content of the memory shared with the driver? >
Thanks for the review. yes, this was flagged by Sashiko while reviewing the previous patch, but I agree the commit message shouldn't present it as a proven firmware mutation bug. The useful part here is just making the validated count the same value used as the loop bound. since It's an optimisation, should I send v2 without Fixes and Cc stable tags? > > > > Read each count once with READ_ONCE() and use the validated snapshot as the > > loop bound. This keeps the loop bounds consistent with the validation and > > prevents the compiler from reloading a firmware-controlled count during > > iteration. > > As an optimisation I'm fine with it, so: > > Reviewed-by: Liviu Dudau <[email protected]> > > Best regards, > Liviu > Best regards, Osama > > > > Fixes: 2718d91816ee ("drm/panthor: Add the FW logical block") > > Cc: [email protected] > > Signed-off-by: Osama Abdelkader <[email protected]> > > --- > > drivers/gpu/drm/panthor/panthor_fw.c | 11 +++++++---- > > 1 file changed, 7 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/gpu/drm/panthor/panthor_fw.c > > b/drivers/gpu/drm/panthor/panthor_fw.c > > index e2fcbd639c3c..6e6da98d795e 100644 > > --- a/drivers/gpu/drm/panthor/panthor_fw.c > > +++ b/drivers/gpu/drm/panthor/panthor_fw.c > > @@ -959,6 +959,7 @@ static int panthor_init_csg_iface(struct panthor_device > > *ptdev, > > u64 shared_section_sz = > > panthor_kernel_bo_size(ptdev->fw->shared_section->mem); > > u64 iface_offset = CSF_GROUP_CONTROL_OFFSET + > > ((u64)csg_idx * glb_iface->control->group_stride); > > + u32 stream_num; > > unsigned int i; > > > > if (iface_offset > shared_section_sz || > > @@ -972,8 +973,8 @@ static int panthor_init_csg_iface(struct panthor_device > > *ptdev, > > csg_iface->output = iface_fw_to_cpu_addr(ptdev, > > csg_iface->control->output_va, > > sizeof(*csg_iface->output)); > > > > - if (csg_iface->control->stream_num < MIN_CS_PER_CSG || > > - csg_iface->control->stream_num > MAX_CS_PER_CSG) > > + stream_num = READ_ONCE(csg_iface->control->stream_num); > > + if (stream_num < MIN_CS_PER_CSG || stream_num > MAX_CS_PER_CSG) > > return -EINVAL; > > > > if (!csg_iface->input || !csg_iface->output) { > > @@ -990,7 +991,7 @@ static int panthor_init_csg_iface(struct panthor_device > > *ptdev, > > } > > } > > > > - for (i = 0; i < csg_iface->control->stream_num; i++) { > > + for (i = 0; i < stream_num; i++) { > > int ret = panthor_init_cs_iface(ptdev, csg_idx, i); > > > > if (ret) > > @@ -1015,6 +1016,7 @@ static int panthor_fw_init_ifaces(struct > > panthor_device *ptdev) > > { > > struct panthor_fw_global_iface *glb_iface = &ptdev->fw->iface.global; > > u64 shared_section_sz = > > panthor_kernel_bo_size(ptdev->fw->shared_section->mem); > > + u32 group_num; > > unsigned int i; > > > > if (!ptdev->fw->shared_section->mem->kmap) > > @@ -1034,17 +1036,17 @@ static int panthor_fw_init_ifaces(struct > > panthor_device *ptdev) > > return -EINVAL; > > } > > > > - if (glb_iface->control->group_num > MAX_CSGS || > > - glb_iface->control->group_num < MIN_CSGS) { > > + group_num = READ_ONCE(glb_iface->control->group_num); > > + if (group_num > MAX_CSGS || group_num < MIN_CSGS) { > > drm_err(&ptdev->base, "Invalid number of control groups"); > > return -EINVAL; > > } > > > > - for (i = 0; i < glb_iface->control->group_num; i++) { > > + for (i = 0; i < group_num; i++) { > > int ret = panthor_init_csg_iface(ptdev, i); > > > > if (ret) > > return ret; > > } > > > > drm_info(&ptdev->base, "CSF FW using interface v%d.%d.%d, Features %#x > > Instrumentation features %#x", > > -- > > 2.43.0 > > > > -- > ==================== > | I would like to | > | fix the world, | > | but they're not | > | giving me the | > \ source code! / > --------------- > ¯\_(ツ)_/¯
