linux-kernel - Re: [PATCH v2 1/9] drm/panthor: Add 64-bit and poll register accessors

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Message-ID: <20250410152822.632b09b8@collabora.com>
Date: Thu, 10 Apr 2025 15:28:22 +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 1/9] drm/panthor: Add 64-bit and poll register
 accessors

On Wed, 9 Apr 2025 14:00:54 +0100
Karunika Choo <karunika.choo@....com> wrote:

> On 21/03/2025 07:48, Boris Brezillon wrote:
> > On Thu, 20 Mar 2025 11:17:33 +0000
> > Karunika Choo <karunika.choo@....com> wrote:
> >  
> >> This patch adds 64-bit register accessors to simplify register access in
> >> Panthor. It also adds 32-bit and 64-bit variants for read_poll_timeout.
> >>
> >> Signed-off-by: Karunika Choo <karunika.choo@....com>
> >> ---
> >>  drivers/gpu/drm/panthor/panthor_regs.h | 55 ++++++++++++++++++++++++++
> >>  1 file changed, 55 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/panthor/panthor_regs.h  
> b/drivers/gpu/drm/panthor/panthor_regs.h
> >> index 42dc3fedb0d4..7ec4a1d04e20 100644
> >> --- a/drivers/gpu/drm/panthor/panthor_regs.h
> >> +++ b/drivers/gpu/drm/panthor/panthor_regs.h
> >> @@ -238,4 +238,59 @@
> >>  #define gpu_read(dev, reg) \
> >>  	readl((dev)->iomem + (reg))
> >>
> >> +#define gpu_read_relaxed(dev, reg) readl_relaxed((dev)->iomem + (reg))
> >> +
> >> +#define gpu_write64(dev, reg, data)                            \
> >> +	do {                                                   \
> >> +		u64 __val = (u64)(data);                       \
> >> +		gpu_write(dev, reg, lower_32_bits(__val));     \
> >> +		gpu_write(dev, reg + 4, upper_32_bits(__val)); \
> >> +	} while (0)  
> >
> > We're not doing funky name concatenation in these macros, so I'd rather
> > have them defined as static inline funcs in panthor_device.h. We
> > probably want to move the gpu_read/write definitions there as well if
> > we do that.  
> 
> I see where you're coming from, and it makes sense. I was thinking it
> might be better to keep it in panthor_regs.h since that's the file we
> include when accessing GPU registers.

Well, yes, but also gpu_write/read() take a panthor_device, which is
defined in panthor_device.h. I guess we can keep those in
panthor_regs.h and include panthor_device.h from panthor_regs.h if
there's no circular inclusion. I'm fine either way.

> That said, we could certainly
> convert them to static inline functions if you prefer.

Yeah, I'd prefer that.

> 
> >> +
> >> +#define gpu_read64(dev, reg) \
> >> +	(gpu_read(dev, reg) | ((u64)gpu_read(dev, reg + 4) << 32))
> >> +
> >> +#define gpu_read64_relaxed(dev, reg)  \
> >> +	(gpu_read_relaxed(dev, reg) | \
> >> +	 ((u64)gpu_read_relaxed(dev, reg + 4) << 32))
> >> +
> >> +#define gpu_read64_sync(dev, reg)                     \
> >> +	({                                            \
> >> +		u32 lo, hi1, hi2;                     \
> >> +		do {                                  \
> >> +			hi1 = gpu_read(dev, reg + 4); \
> >> +			lo = gpu_read(dev, reg);      \
> >> +			hi2 = gpu_read(dev, reg + 4); \
> >> +		} while (hi1 != hi2);                 \
> >> +		lo | ((u64)hi2 << 32);                \
> >> +	})  
> >
> > I would name that one gpu_read64_counter and make it a static inline
> > function. Note that we already have panthor_gpu_read_64bit_counter()
> > which does the same thing, so maybe move it there and rename it along
> > the way.  
> 
> Happy to rename this to gpu_read64_counter in v3, if you're okay with
> us keeping the macros/functions in this file.

Renaming the function is orthogonal to moving its definition to a
different header, no? I'm not sure I see why one depends on the other.