linux-kernel - Re: [PATCH] i2c: exynos5: Preserve high speed master code

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Date:   Tue, 16 Feb 2021 08:51:41 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Mårten Lindahl <marten.lindahl@...s.com>
Cc:     kernel@...s.com,
        Mårten Lindahl <martenli@...s.com>,
        linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: exynos5: Preserve high speed master code

On Mon, Feb 15, 2021 at 08:03:21PM +0100, Mårten Lindahl wrote:
> From: Mårten Lindahl <martenli@...s.com>
> 
> When the controller starts to send a message with the MASTER_ID field
> set (high speed), the whole I2C_ADDR register is overwritten including
> MASTER_ID as the SLV_ADDR_MAS field is set.

Are you here describing bug in driver or hardware (the controller?)?
Looking at the code, I think the driver, but description got me
confused.

> 
> This patch preserves already written fields in I2C_ADDR when writing
> SLV_ADDR_MAS.
> 
> Signed-off-by: Mårten Lindahl <martenli@...s.com>
> ---
>  drivers/i2c/busses/i2c-exynos5.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-exynos5.c b/drivers/i2c/busses/i2c-exynos5.c
> index 20a9881a0d6c..f2d04c241299 100644
> --- a/drivers/i2c/busses/i2c-exynos5.c
> +++ b/drivers/i2c/busses/i2c-exynos5.c
> @@ -606,6 +606,7 @@ static void exynos5_i2c_message_start(struct exynos5_i2c *i2c, int stop)
>  	u32 i2c_ctl;
>  	u32 int_en = 0;
>  	u32 i2c_auto_conf = 0;
> +	u32 i2c_addr = 0;
>  	u32 fifo_ctl;
>  	unsigned long flags;
>  	unsigned short trig_lvl;
> @@ -640,7 +641,12 @@ static void exynos5_i2c_message_start(struct exynos5_i2c *i2c, int stop)
>  		int_en |= HSI2C_INT_TX_ALMOSTEMPTY_EN;
>  	}
>  
> -	writel(HSI2C_SLV_ADDR_MAS(i2c->msg->addr), i2c->regs + HSI2C_ADDR);
> +	i2c_addr = HSI2C_SLV_ADDR_MAS(i2c->msg->addr);
> +
> +	if (i2c->op_clock >= I2C_MAX_FAST_MODE_PLUS_FREQ)
> +		i2c_addr |= readl(i2c->regs + HSI2C_ADDR);

Any reason why not "|= MASTER_ID(i2c->adap.nr)" here instead of more
expensive IO read? It's quite important because your current code will
bitwise-or old I2C slave address with a new one... This should break
during tests with multiple I2C slave devices, shouldn't it?

On which HW did you test it?

Best regards,
Krzysztof


> +
> +	writel(i2c_addr, i2c->regs + HSI2C_ADDR);