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Date: Wed, 10 Jan 2024 17:00:30 +0100
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] i2c: cadence: Avoid fifo clear after start
Content-Language: en-US
To: Sai Pavan Boddu <sai.pavan.boddu@amd.com>, linux-kernel@vger.kernel.org,
 linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Cc: Andi Shyti <andi.shyti@kernel.org>, Lars-Peter Clausen <lars@metafoo.de>,
 Wolfram Sang <wsa@kernel.org>
References: <20240105125258.2470397-1-sai.pavan.boddu@amd.com>
From: Michal Simek <michal.simek@amd.com>
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On 1/5/24 13:52, Sai Pavan Boddu wrote:
> Driver unintentionally programs ctrl reg to clear fifo which is
> happening after start of transaction, this was not the case previously
> as it was read-modified-write. This issue breaks i2c reads on QEMU as
> i2c-read is done before guest starts programming ctrl register.
> 
> Fixes: ff0cf7bca6309 ("i2c: cadence: Remove unnecessary register reads")
> Signed-off-by: Sai Pavan Boddu <sai.pavan.boddu@amd.com>
> ---
>   drivers/i2c/busses/i2c-cadence.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index de3f58b60dce..6f7d753a8197 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -633,6 +633,7 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
>   
>   	if (hold_clear) {
>   		ctrl_reg &= ~CDNS_I2C_CR_HOLD;
> +		ctrl_reg &= ~CDNS_I2C_CR_CLR_FIFO;
>   		/*
>   		 * In case of Xilinx Zynq SOC, clear the HOLD bit before transfer size
>   		 * register reaches '0'. This is an IP bug which causes transfer size

Acked-by: Michal Simek <michal.simek@amd.com>

Thanks,
Michal