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

[Karunika Choo]

On 21/03/2025 08:02, Boris Brezillon wrote:
> On Thu, 20 Mar 2025 11:17:37 +0000
> Karunika Choo <karunika.choo@xxxxxxx> 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@xxxxxxx>
>> ---
>>  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)))
>