linux-kernel - Re: [PATCH 04/10] drm/panthor: add mmu_hw_cmd

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Message-ID: <c4f100fe-88a5-4409-a728-6b296ce23877@arm.com>
Date: Thu, 2 Oct 2025 11:41:31 +0100
From: Steven Price <steven.price@....com>
To: Chia-I Wu <olvaffe@...il.com>,
 Boris Brezillon <boris.brezillon@...labora.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>,
 Grant Likely <grant.likely@...aro.org>, Heiko Stuebner <heiko@...ech.de>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/10] drm/panthor: add mmu_hw_cmd_update

On 16/09/2025 22:08, Chia-I Wu wrote:
> Add a simple helper for the UPDATE command.

Why? There's only two call sites, so we're not saving much (indeed the
diffstat shows we've got over twice as many lines)...

> 
> Signed-off-by: Chia-I Wu <olvaffe@...il.com>
> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 33 +++++++++++++++++++--------
>  1 file changed, 23 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 953348f9afdb8..727339d80d37e 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -545,6 +545,27 @@ static int write_cmd(struct panthor_device *ptdev, u32 as_nr, u32 cmd)
>  	return status;
>  }
>  
> +/**
> + * mmu_hw_cmd_update() - Issue an UPDATE command
> + * @ptdev: Device.
> + * @as_nr: AS to issue command to.
> + * @transtab: Addr of the translation table.
> + * @transcfg: Bitmask of AS_TRANSCFG_*.
> + * @memattr: Bitmask of AS_MEMATTR_*.
> + *
> + * Issue an UPDATE command to invalidate MMU caches and update the translation
> + * table.
> + */
> +static int mmu_hw_cmd_update(struct panthor_device *ptdev, u32 as_nr, u64 transtab, u64 transcfg,
> +			     u64 memattr)
> +{
> +	gpu_write64(ptdev, AS_TRANSTAB(as_nr), transtab);
> +	gpu_write64(ptdev, AS_MEMATTR(as_nr), memattr);
> +	gpu_write64(ptdev, AS_TRANSCFG(as_nr), transcfg);
> +
> +	return write_cmd(ptdev, as_nr, AS_COMMAND_UPDATE);
> +}
> +
>  /**
>   * mmu_hw_cmd_lock() - Issue a LOCK command
>   * @ptdev: Device.
> @@ -674,11 +695,7 @@ static int panthor_mmu_as_enable(struct panthor_device *ptdev, u32 as_nr,
>  	if (ret)
>  		return ret;
>  
> -	gpu_write64(ptdev, AS_TRANSTAB(as_nr), transtab);
> -	gpu_write64(ptdev, AS_MEMATTR(as_nr), memattr);
> -	gpu_write64(ptdev, AS_TRANSCFG(as_nr), transcfg);
> -
> -	return write_cmd(ptdev, as_nr, AS_COMMAND_UPDATE);
> +	return mmu_hw_cmd_update(ptdev, as_nr, transtab, transcfg, memattr);
>  }
>  
>  static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr)
> @@ -689,11 +706,7 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr)
>  	if (ret)
>  		return ret;
>  
> -	gpu_write64(ptdev, AS_TRANSTAB(as_nr), 0);
> -	gpu_write64(ptdev, AS_MEMATTR(as_nr), 0);
> -	gpu_write64(ptdev, AS_TRANSCFG(as_nr), AS_TRANSCFG_ADRMODE_UNMAPPED);
> -
> -	return write_cmd(ptdev, as_nr, AS_COMMAND_UPDATE);
> +	return mmu_hw_cmd_update(ptdev, as_nr, 0, AS_TRANSCFG_ADRMODE_UNMAPPED, 0);

... and here in particular the code is less clear. It's no longer
obvious which registers we're writing 0 to.

Thanks,
Steve

>  }
>  
>  static u32 panthor_mmu_fault_mask(struct panthor_device *ptdev, u32 value)