linux-kernel - Re: [PATCH v4 2/5] mmc: sdhci: always obey programmable clock config in preset value

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Message-ID: <fe01b20d-779b-1e2c-7702-5a4702900d84@intel.com>
Date:   Wed, 4 Aug 2021 13:52:21 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Kevin Liu <kliu5@...vell.com>,
        Michal Simek <michal.simek@...inx.com>,
        Suneel Garapati <suneel.garapati@...inx.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Al Cooper <alcooperx@...il.com>
Subject: Re: [PATCH v4 2/5] mmc: sdhci: always obey programmable clock config
 in preset value

On 25/07/21 12:20 pm, Michał Mirosław wrote:
> When host controller uses programmable clock presets but doesn't
> advertise programmable clock support, we can only guess what frequency
> it generates. Let's at least return correct SDHCI_PROG_CLOCK_MODE bit
> value in this case.

If the preset value doesn't make sense, why use it at all?

> 
> Fixes: 52983382c74f ("mmc: sdhci: enhance preset value function")
> Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> ---
> v4: no changes
> v3: added a comment for this case
> v2: no changes
> ---
>  drivers/mmc/host/sdhci.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index c7438dd13e3e..3ab60e7f936b 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1859,11 +1859,14 @@ u16 sdhci_calc_clk(struct sdhci_host *host, unsigned int clock,
>  
>  			pre_val = sdhci_get_preset_value(host);
>  			div = FIELD_GET(SDHCI_PRESET_SDCLK_FREQ_MASK, pre_val);
> -			if (host->clk_mul &&
> -				(pre_val & SDHCI_PRESET_CLKGEN_SEL)) {
> +			if (pre_val & SDHCI_PRESET_CLKGEN_SEL) {
>  				clk = SDHCI_PROG_CLOCK_MODE;
>  				real_div = div + 1;
>  				clk_mul = host->clk_mul;
> +				if (!clk_mul) {
> +					/* The clock frequency is unknown. Assume undivided base. */
> +					clk_mul = 1;
> +				}
>  			} else {
>  				real_div = max_t(int, 1, div << 1);
>  			}
>