Re: [PATCH v4] i2c: sh_mobile: implement atomic transfers

[Wolfram Sang <wsa@the-dreams.de>]

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Hi Uli,

On Mon, Sep 28, 2020 at 05:59:50PM +0200, Ulrich Hecht wrote:
> Implements atomic transfers to fix reboot/shutdown on r8a7790 Lager and
> similar boards.
> 
> Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
> Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

It works, but I have two comments and two questions:

> @@ -581,10 +585,12 @@ static void start_ch(struct sh_mobile_i2c_data *pd, struct i2c_msg *usr_msg,
>  	pd->pos = -1;
>  	pd->sr = 0;
>  
> +	if (pd->atomic_xfer)
> +		return;
> +
>  	pd->dma_buf = i2c_get_dma_safe_msg_buf(pd->msg, 8);
>  	if (pd->dma_buf)
>  		sh_mobile_i2c_xfer_dma(pd);
> -

This blank line should stay.

...

> +		if (pd->atomic_xfer) {
> +			unsigned long j = jiffies + pd->adap.timeout;
> +
> +			time_left = time_before_eq(jiffies, j);
> +			while (time_left &&
> +			       !(pd->sr & (ICSR_TACK | SW_DONE))) {
> +				unsigned char sr = iic_rd(pd, ICSR);
> +
> +				if (sr & (ICSR_AL   | ICSR_TACK |
> +					  ICSR_WAIT | ICSR_DTE)) {
> +					sh_mobile_i2c_isr(0, pd);
> +					udelay(150);
> +				} else {
> +					cpu_relax();
> +				}

Is it 100% safe to call cpu_relax() that late? Aren't interrupts
disabled? What is waking the CPU again? And where does the value 150us
come from?

> +				time_left = time_before_eq(jiffies, j);
> +			}
> +		} else {
> +			/* The interrupt handler takes care of the rest... */
> +			time_left = wait_event_timeout(pd->wait,
> +					pd->sr & (ICSR_TACK | SW_DONE),
> +					pd->adap.timeout);
> +
> +			/* 'stop_after_dma' tells if DMA xfer was complete */
> +			i2c_put_dma_safe_msg_buf(pd->dma_buf, pd->msg,
> +						 pd->stop_after_dma);
>  

This blank line can go.

Thanks and regards,

   Wolfram


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