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); > + > + 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); > } >
