On Fri, Dec 19, 2025 at 7:31 AM Steven Price <[email protected]> wrote: > > On 17/12/2025 17:03, Nicolas Frattaroli wrote: > > On some platforms, notably MediaTek MT8196, the shader_present bitmask > > in the Mali GPU register for it has cores enabled that may be faulty. > > The true shader_present bitmask is found in an efuse instead. > > > > Implement reading shader_present from an nvmem cell if one is present, > > falling back to the Mali register if it's absent. The error codes are > > trickled up through to the probe function so that probe deferral works. > > > > Signed-off-by: Nicolas Frattaroli <[email protected]> > > Reviewed-by: Steven Price <[email protected]> > > [Although I really hope other vendors don't do this - the hardware is > broken!] > > Although one NIT below if you respin for other reasons... > > > --- > > drivers/gpu/drm/panthor/panthor_hw.c | 63 > > ++++++++++++++++++++++++++++++++---- > > 1 file changed, 57 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/gpu/drm/panthor/panthor_hw.c > > b/drivers/gpu/drm/panthor/panthor_hw.c > > index 87ebb7ae42c4..eb44c8b108aa 100644 > > --- a/drivers/gpu/drm/panthor/panthor_hw.c > > +++ b/drivers/gpu/drm/panthor/panthor_hw.c > > @@ -1,6 +1,7 @@ > > // SPDX-License-Identifier: GPL-2.0 or MIT > > /* Copyright 2025 ARM Limited. All rights reserved. */ > > > > +#include <linux/nvmem-consumer.h> > > #include <drm/drm_print.h> > > > > #include "panthor_device.h" > > @@ -109,7 +110,52 @@ static char *get_gpu_model_name(struct panthor_device > > *ptdev) > > return "(Unknown Mali GPU)"; > > } > > > > -static void panthor_gpu_info_init(struct panthor_device *ptdev) > > +static int overload_shader_present(struct panthor_device *ptdev) > > +{ > > + struct device *dev = ptdev->base.dev; > > + struct nvmem_cell *cell = nvmem_cell_get(dev, "shader-present"); > > + ssize_t len; > > + void *buf; > > + int ret; > > + > > + if (IS_ERR(cell)) { > > + /* On platforms without this cell, use the Mali register */ > > + if (PTR_ERR(cell) == -ENOENT) > > + return 0; > > + > > + return dev_err_probe(dev, PTR_ERR(cell), > > + "Failed to get shader-present nvmem > > cell\n"); > > + } > > + > > + buf = nvmem_cell_read(cell, &len); > > + if (IS_ERR(buf)) { > > + ret = dev_err_probe(dev, PTR_ERR(buf), > > + "Failed to read shader-present nvmem > > cell\n"); > > + goto err_put_cell; > > + } > > + > > + if (!len || len > 8) { > > + ret = dev_err_probe(dev, -EINVAL, "shader-present cell can't > > be length %ld\n", > > + len); > > + goto err_free; > > + } > > + > > + memcpy(&ptdev->gpu_info.shader_present, buf, len); When len is 4, this is neither overriding nor masking. I might suggest switching to nvmem_cell_read_variable_le_u64 for simplicity.
Either way, Reviewed-by: Chia-I Wu <[email protected]> > > + > > + kfree(buf); > > + nvmem_cell_put(cell); > > + > > + return 0; > > + > > +err_free: > > + kfree(buf); > > +err_put_cell: > > + nvmem_cell_put(cell); > > + > > + return ret; > > +} > > Rather than repeating the clean up, you can do something like: > > { > void *buf = NULL; > int ret = 0 > > if (IS_ERR(cell)) { > ret = dev_err_probe(...); > goto out; > } > > buf = nvmem_cell_read(); > if (IS_ERR(buf)) { > ret = dev_err_probe(...); > goto out; > } > > if (!len || len > 8) { > ret = dev_err_probe(...); > goto out; > } > > memcpy(); > > out: > if (!IS_ERR(buf)) > kfree(buf); > if (!IS_ERR(cell)) > nvmem_cell_put(cell); > > return ret; > } > > That avoids mistakes when adding a new operation into the sequence. Or > you can use the fancy new cleanup helpers, but that feels overkill here. > But equally I'm ok if you leave the code as is - it's simple enough and > the conversation can be done later if we need it. > > Thanks, > Steve > > > + > > +static int panthor_gpu_info_init(struct panthor_device *ptdev) > > { > > unsigned int i; > > > > @@ -143,13 +189,18 @@ static void panthor_gpu_info_init(struct > > panthor_device *ptdev) > > ptdev->gpu_info.tiler_present = gpu_read64(ptdev, > > GPU_TILER_PRESENT); > > ptdev->gpu_info.l2_present = gpu_read64(ptdev, > > GPU_L2_PRESENT); > > } > > + > > + return overload_shader_present(ptdev); > > } > > > > -static void panthor_hw_info_init(struct panthor_device *ptdev) > > +static int panthor_hw_info_init(struct panthor_device *ptdev) > > { > > u32 major, minor, status; > > + int ret; > > > > - panthor_gpu_info_init(ptdev); > > + ret = panthor_gpu_info_init(ptdev); > > + if (ret) > > + return ret; > > > > major = GPU_VER_MAJOR(ptdev->gpu_info.gpu_id); > > minor = GPU_VER_MINOR(ptdev->gpu_info.gpu_id); > > @@ -172,6 +223,8 @@ static void panthor_hw_info_init(struct panthor_device > > *ptdev) > > "shader_present=0x%0llx l2_present=0x%0llx > > tiler_present=0x%0llx", > > ptdev->gpu_info.shader_present, ptdev->gpu_info.l2_present, > > ptdev->gpu_info.tiler_present); > > + > > + return 0; > > } > > > > static int panthor_hw_bind_device(struct panthor_device *ptdev) > > @@ -218,7 +271,5 @@ int panthor_hw_init(struct panthor_device *ptdev) > > if (ret) > > return ret; > > > > - panthor_hw_info_init(ptdev); > > - > > - return 0; > > + return panthor_hw_info_init(ptdev); > > } > > >
