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

Karunika Choo
2025-04-10T16:49:28Z

On 10/04/2025 14:28, Boris Brezillon wrote:
> On Wed, 9 Apr 2025 14:00:54 +0100
> Karunika Choo <karunika.choo@arm.com> wrote:
>
>> On 21/03/2025 07:48, Boris Brezillon wrote:
>>> On Thu, 20 Mar 2025 11:17:33 +0000
>>> Karunika Choo <karunika.choo@arm.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@arm.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.
>

Apologies for the back-and-forth. You’re absolutely right—it’s a good
point that struct panthor_device is defined in panthor_device.h. I
have moved these functions there as static inline functions, in a
separate patch outside this series.

Link: https://lore.kernel.org/lkml/20250410163546.919749-1-karunika.choo@arm.com/

Kind regards,
Karunika Choo

>>
>>>> +
>>>> +#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.