Re: [PATCH 4/4] nvme: apple: Drop the PRP null check chicken bit

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Janne Grunau <j@jannau.net>
> Date: Fri, 04 Sep 2026 21:22:42 +0200
> 
> Now that we program the DMA direction correctly the NULL check that used
> to make commands fail passes. Another side effect of this bit was that
> non-align buffers on the admin queue were silently allowed and that's
> been fixed now as well and we this don't need this chicken bit anymore.
> More importantly, starting with the firmware installed with macOS 15,
> which is required for M4 but can also be installed on the previous SoCs,
> the controller no longer exposes this control register and any access
> SErrors instead. Just drop the write entirely.
> 
> Based on Linux kernel commit 8ce883fd068b ("nvme-apple: Drop the PRP
> null check chicken bit").

Reviewed-by: Mark Kettenis <kettenis@openbsd.org>

> Link: https://lore.kernel.org/asahi/20260806-b4-nvme-fwabi-v1-6-bde19ce8db04@kernel.org/
> Fixes: 50333c94f2de ("nvme: apple: Add driver for Apple NVMe storage controller")
> Signed-off-by: Janne Grunau <j@jannau.net>
> ---
>  drivers/nvme/nvme_apple.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/nvme/nvme_apple.c b/drivers/nvme/nvme_apple.c
> index 54821f80c81..948a56e518b 100644
> --- a/drivers/nvme/nvme_apple.c
> +++ b/drivers/nvme/nvme_apple.c
> @@ -26,8 +26,6 @@
>  #define ANS_BOOT_STATUS		0x01300
>  #define  ANS_BOOT_STATUS_OK	0xde71ce55
>  #define ANS_MODESEL		0x01304
> -#define ANS_UNKNOWN_CTRL	0x24008
> -#define  ANS_PRP_NULL_CHECK	(1 << 11)
>  #define ANS_LINEAR_SQ_CTRL	0x24908
>  #define  ANS_LINEAR_SQ_CTRL_EN	(1 << 0)
>  #define ANS_ASQ_DB		0x2490c
> @@ -257,9 +255,6 @@ static int apple_nvme_probe(struct udevice *dev)
>  	writel(((ANS_MAX_QUEUE_DEPTH << 16) | ANS_MAX_QUEUE_DEPTH),
>  	       priv->base + ANS_MAX_PEND_CMDS_CTRL);
>  
> -	writel(readl(priv->base + ANS_UNKNOWN_CTRL) & ~ANS_PRP_NULL_CHECK,
> -	       priv->base + ANS_UNKNOWN_CTRL);
> -
>  	strcpy(priv->ndev.vendor, "Apple");
>  
>  	writel((ANS_NVMMU_TCB_SIZE / ANS_NVMMU_TCB_PITCH) - 1,
> 
> -- 
> 2.55.0
> 
>