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

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Message-ID: <20250410153729.1fb0444c@collabora.com>
Date: Thu, 10 Apr 2025 15:37:29 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Karunika Choo <karunika.choo@....com>
Cc: dri-devel@...ts.freedesktop.org, nd@....com, Steven Price
 <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/9] drm/panthor: Make getting GPU model name simple
 and extensible

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

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