linux-kernel - Re: [PATCH] i2c: cadence: Avoid fifo clear after start

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Date: Wed, 10 Jan 2024 17:00:30 +0100
From: Michal Simek <michal.simek@....com>
To: Sai Pavan Boddu <sai.pavan.boddu@....com>, linux-kernel@...r.kernel.org,
 linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc: Andi Shyti <andi.shyti@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>,
 Wolfram Sang <wsa@...nel.org>
Subject: Re: [PATCH] i2c: cadence: Avoid fifo clear after start



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@....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@....com>

Thanks,
Michal