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From: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Kevin Liu <kliu5@marvell.com>,
	Michal Simek <michal.simek@xilinx.com>,
	Suneel Garapati <suneel.garapati@xilinx.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
	Al Cooper <alcooperx@gmail.com>
Subject: Re: [PATCH v4 2/5] mmc: sdhci: always obey programmable clock config in preset value
Date: Sat, 7 Aug 2021 16:05:06 +0200	[thread overview]
Message-ID: <YQ6TEhMLXH/4r4BS@qmqm.qmqm.pl> (raw)
In-Reply-To: <fe01b20d-779b-1e2c-7702-5a4702900d84@intel.com>

On Wed, Aug 04, 2021 at 01:52:21PM +0300, Adrian Hunter wrote:
> 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?

If I understand the spec correctly, when the preset value is used the
values in Clock Control register are ignored by the module and so the
module can also actually use a different clock source than the ones
available to the driver directly. So either way the driver can't be
sure of the exact frequencu used. This is a cleanup to remove a case
when the code ignores a bit's value based on other unspecified assumptions.

[...]
> > --- 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);
> >  			}

  reply	other threads:[~2021-08-07 14:06 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-25  9:20 [PATCH v4 0/5] SDHCI clock handling fixes and cleanups Michał Mirosław
2021-07-25  9:20 ` [PATCH v4 1/5] mmc: sdhci: fix base clock usage in preset value Michał Mirosław
2021-08-04 10:50   ` Adrian Hunter
2021-07-25  9:20 ` [PATCH v4 2/5] mmc: sdhci: always obey programmable clock config " Michał Mirosław
2021-08-04 10:52   ` Adrian Hunter
2021-08-07 14:05     ` Michał Mirosław [this message]
2021-08-12  9:54       ` Adrian Hunter
2021-07-25  9:20 ` [PATCH v4 3/5] mmc: sdhci: fix SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN Michał Mirosław
2021-08-04 11:06   ` Adrian Hunter
2021-08-07 14:08     ` Michał Mirosław
2021-07-25  9:20 ` [PATCH v4 5/5] mmc: sdhci: simplify v2/v3+ clock calculation Michał Mirosław
2021-08-04 12:40   ` Adrian Hunter
2021-08-07 15:39     ` Michał Mirosław
2021-07-25  9:20 ` [PATCH v4 4/5] mmc: sdhci: move SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN frequency limit Michał Mirosław
2021-08-04 12:33   ` Adrian Hunter
2021-08-07 14:12     ` Michał Mirosław
2021-08-12 10:01       ` Adrian Hunter

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