Re: [PATCH v2 5/9] drm/panthor: Make getting GPU model name simple and extensible

Boris Brezillon
2025-04-10T13:37:36Z

On Thu, 10 Apr 2025 14:20:59 +0100
Karunika Choo <karunika.choo@arm.com> wrote:

> On 21/03/2025 08:02, Boris Brezillon wrote:
> > On Thu, 20 Mar 2025 11:17:37 +0000
> > Karunika Choo <karunika.choo@arm.com> wrote:
> >
> >> This patch replaces the previous panthor_model structure with a simple
> >> switch case based on the product_id, which is in the format of:
> >> ((arch_major << 24) | product_major)
> >>
> >> This not only simplifies the comparison, but also allows extending the
> >> function to accommodate naming differences based on GPU features.
> >>
> >> Signed-off-by: Karunika Choo <karunika.choo@arm.com>
> >> ---
> >> drivers/gpu/drm/panthor/panthor_hw.c | 63 +++++++-------------------
> >> drivers/gpu/drm/panthor/panthor_regs.h | 1 +
> >> 2 files changed, 18 insertions(+), 46 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/panthor/panthor_hw.c b/drivers/gpu/drm/panthor/panthor_hw.c
> >> index 4cc4b0d5382c..12183c04cd21 100644
> >> --- a/drivers/gpu/drm/panthor/panthor_hw.c
> >> +++ b/drivers/gpu/drm/panthor/panthor_hw.c
> >> @@ -5,40 +5,6 @@
> >> #include "panthor_hw.h"
> >> #include "panthor_regs.h"
> >>
> >> -/**
> >> - * struct panthor_model - GPU model description
> >> - */
> >> -struct panthor_model {
> >> - /** @name: Model name. */
> >> - const char *name;
> >> -
> >> - /** @arch_major: Major version number of architecture. */
> >> - u8 arch_major;
> >> -
> >> - /** @product_major: Major version number of product. */
> >> - u8 product_major;
> >> -};
> >> -
> >> -/**
> >> - * GPU_MODEL() - Define a GPU model. A GPU product can be uniquely identified
> >> - * by a combination of the major architecture version and the major product
> >> - * version.
> >> - * @_name: Name for the GPU model.
> >> - * @_arch_major: Architecture major.
> >> - * @_product_major: Product major.
> >> - */
> >> -#define GPU_MODEL(_name, _arch_major, _product_major) \
> >> -{\
> >> - .name = __stringify(_name), \
> >> - .arch_major = _arch_major, \
> >> - .product_major = _product_major, \
> >> -}
> >> -
> >> -static const struct panthor_model gpu_models[] = {
> >> - GPU_MODEL(g610, 10, 7),
> >> - {},
> >> -};
> >> -
> >> static void arch_10_8_gpu_info_init(struct panthor_device *ptdev)
> >> {
> >> unsigned int i;
> >> @@ -66,29 +32,34 @@ static void arch_10_8_gpu_info_init(struct panthor_device *ptdev)
> >> ptdev->gpu_info.l2_present = gpu_read64(ptdev, GPU_L2_PRESENT_LO);
> >> }
> >>
> >> +static char *get_gpu_model_name(struct panthor_device *ptdev)
> >> +{
> >> + const u32 gpu_id = ptdev->gpu_info.gpu_id;
> >> + const u32 product_id = GPU_PROD_ID_MAKE(GPU_ARCH_MAJOR(gpu_id),
> >> + GPU_PROD_MAJOR(gpu_id));
> >> +
> >> + switch (product_id) {
> >> + case GPU_PROD_ID_MAKE(10, 7):
> >> + return "Mali-G610";
> >> + }
> >
> > I a big fan of these ever growing switch statements with nested
> > conditionals. Could we instead add an optional ::get_variant() callback
> > in panthor_model and have the following formatting:
> >
> > "Mali-%s%s%s", model->name,
> > model->get_variant ? "-" : "",
> > model->get_variant ? model->get_variant() : ""
> >
>
> While that’s certainly an option, I wonder if it’s better to avoid
> additional string formatting when it’s not strictly necessary. The
> switch cases provide a straightforward GPU name without needing to
> handle conditional "-" separators or similar.
>
> Also, with the current approach, if a GPU is misconfigured with an
> incorrect product_major for its core count, the switch’s fallthrough
> helps ensure the correct name is still returned. A model->get_variant()
> callback wouldn’t give us that same flexibility to adjust the name based
> on such mismatches.

Fair enough. I guess we can live with this sort of switch statement for
the name selection. Hopefully the variants are rare enough that it
doesn't go too wild.