linux-kernel - Re: [PATCH 2/3] mmc:sunxi-mmc:fix clock division for timing mode

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Date:   Wed, 12 Jan 2022 10:20:54 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Michael Wu <michael@...winnertech.com>
Cc:     ulf.hansson@...aro.org, wens@...e.org, samuel@...lland.org,
        andre.przywara@....com, jernej.skrabec@...il.com,
        linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mmc:sunxi-mmc:fix clock division for timing mode

Hi Michael,

Thanks for your patch

On Wed, Dec 22, 2021 at 11:15:21AM +0800, Michael Wu wrote:
> When use new timings,all speed mode requires a doubled module clock
> if speed mode is ddr,requires a four times module clock
> When use old timings,only 8 bit ddr requires a doubled module clock
> 
> Signed-off-by: Michael Wu <michael@...winnertech.com>
> ---
>  drivers/mmc/host/sunxi-mmc.c | 27 +++++++++++++++------------
>  1 file changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
> index afeefead6501..7b47ec453fb6 100644
> --- a/drivers/mmc/host/sunxi-mmc.c
> +++ b/drivers/mmc/host/sunxi-mmc.c
> @@ -774,20 +774,23 @@ static int sunxi_mmc_clk_set_rate(struct sunxi_mmc_host *host,
>  	if (!ios->clock)
>  		return 0;
>  
> -	/*
> -	 * Under the old timing mode, 8 bit DDR requires the module
> -	 * clock to be double the card clock. Under the new timing
> -	 * mode, all DDR modes require a doubled module clock.
> -	 *
> -	 * We currently only support the standard MMC DDR52 mode.
> -	 * This block should be updated once support for other DDR
> -	 * modes is added.
> +	/**
> +	 * When use new timings, all speed mode requires a doubled module clock.
> +	 * if speed mode is ddr, requires a four times module clock.
> +	 * When use old timings, only 8 bit ddr requires a doubled module clock.
>  	 */

I found the original comment to be clearer, maybe we can change it to
something like:

    /*
     * Under the old timing mode, 8 bit DDR requires the module
     * clock to be double the card clock. Under the new timing
     * mode, all modes require a doubled module clock, and DDR modes
     * require a quadrupled module clock.
     *
     * ...

> -	if (ios->timing == MMC_TIMING_MMC_DDR52 &&
> -	    (host->use_new_timings ||
> -	     ios->bus_width == MMC_BUS_WIDTH_8)) {
> -		div = 2;
> +	if (host->use_new_timings) {
>  		clock <<= 1;
> +		if (ios->timing == MMC_TIMING_MMC_DDR52) {
> +			div = 2;

Shouldn't that be 4?

> +			clock <<= 1;
> +		}
> +	} else {
> +		if (ios->timing == MMC_TIMING_MMC_DDR52 &&
> +				(ios->bus_width == MMC_BUS_WIDTH_8)) {

This creates some checkpatch.pl --strict warnings

Maxime

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