Re: [PATCH v2 2/6] i2c: spacemit: remove stop function to avoid bus error

From: Aurelien Jarno <aurelien@aurel32.net>
To: Troy Mitchell <troy.mitchell@linux.spacemit.com>
Cc: Andi Shyti <andi.shyti@kernel.org>, Yixun Lan <dlan@gentoo.org>,
	Alex Elder <elder@riscstar.com>,
	Troy Mitchell <troymitchell988@gmail.com>,
	linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, spacemit@lists.linux.dev
Subject: Re: [PATCH v2 2/6] i2c: spacemit: remove stop function to avoid bus error
Date: Thu, 25 Sep 2025 22:11:41 +0200	[thread overview]
Message-ID: <aNWh_dfyfCsqZ8av@aurel32.net> (raw)
In-Reply-To: <20250925-k1-i2c-atomic-v2-2-46dc13311cda@linux.spacemit.com>

On 2025-09-25 10:02, Troy Mitchell wrote:
> Previously, STOP handling was split into two separate steps:
>   1) clear TB/STOP/START/ACK bits
>   2) issue STOP by calling spacemit_i2c_stop()
> 
> This left a small window where the control register was updated
> twice, which can confuse the controller. While this race has not
> been observed with interrupt-driven transfers, it reliably causes
> bus errors in PIO mode.
> 
> Inline the STOP sequence into the IRQ handler and ensure that
> control register bits are updated atomically in a single writel().
> 
> Fixes: 5ea558473fa31 ("i2c: spacemit: add support for SpacemiT K1 SoC")
> Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
> ---
>  drivers/i2c/busses/i2c-k1.c | 26 +++++++-------------------
>  1 file changed, 7 insertions(+), 19 deletions(-)

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                     http://aurel32.net