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

Karunika Choo
2025-04-10T13:21:19Z

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.

Kind regards,
Karunika Choo

>> +
>> + return "(Unknown Mali GPU)";
>> +}
>> +
>> static void panthor_gpu_init_info(struct panthor_device *ptdev)
>> {
>> - const struct panthor_model *model;
>> - u32 arch_major, product_major;
>> + const char *gpu_model_name = get_gpu_model_name(ptdev);
>> u32 major, minor, status;
>>
>> ptdev->hw->ops.gpu_info_init(ptdev);
>>
>> - arch_major = GPU_ARCH_MAJOR(ptdev->gpu_info.gpu_id);
>> - product_major = GPU_PROD_MAJOR(ptdev->gpu_info.gpu_id);
>> major = GPU_VER_MAJOR(ptdev->gpu_info.gpu_id);
>> minor = GPU_VER_MINOR(ptdev->gpu_info.gpu_id);
>> status = GPU_VER_STATUS(ptdev->gpu_info.gpu_id);
>>
>> - for (model = gpu_models; model->name; model++) {
>> - if (model->arch_major == arch_major &&
>> - model->product_major == product_major)
>> - break;
>> - }
>> -
>> drm_info(&ptdev->base,
>> - "mali-%s id 0x%x major 0x%x minor 0x%x status 0x%x",
>> - model->name ?: "unknown", ptdev->gpu_info.gpu_id >> 16,
>> + "%s id 0x%x major 0x%x minor 0x%x status 0x%x",
>> + gpu_model_name, ptdev->gpu_info.gpu_id >> 16,
>> major, minor, status);
>>
>> drm_info(&ptdev->base,
>> diff --git a/drivers/gpu/drm/panthor/panthor_regs.h b/drivers/gpu/drm/panthor/panthor_regs.h
>> index ba452c1dd644..d9e0769d6f1a 100644
>> --- a/drivers/gpu/drm/panthor/panthor_regs.h
>> +++ b/drivers/gpu/drm/panthor/panthor_regs.h
>> @@ -20,6 +20,7 @@
>> #define GPU_VER_STATUS(x) ((x) & GENMASK(3, 0))
>>
>> #define GPU_ARCH_ID_MAKE(major, minor, rev) (((major) << 16) | ((minor) << 8) | (rev))
>> +#define GPU_PROD_ID_MAKE(arch_major, prod_major) (((arch_major) << 24) | (prod_major))
>>
>> #define GPU_L2_FEATURES 0x4
>> #define GPU_L2_FEATURES_LINE_SIZE(x) (1 << ((x) & GENMASK(7, 0)))
>