linux-kernel - Re: [PATCH] i2c: designware: Do not require clock when SSCN and FFCN are provided

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Date:	Wed, 16 Dec 2015 16:28:10 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	wsa@...-dreams.de, lho@....com, Ken.Xue@....com,
	linux-i2c@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH] i2c: designware: Do not require clock when SSCN and FFCN
 are provided

On Wed, Dec 16, 2015 at 08:11:12AM -0600, Suravee Suthikulpanit wrote:
> >The clk framework should work fine if the returned clock is NULL (which
> >I think is your case).
> >
> >The driver gates clocks when the device is suspended and on Intel LPSS
> >there actually is a clock that gets gated.
> >
> >>[..]
> >>@@ -203,13 +223,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
> >>  		dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
> >>  			DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_FAST;
> >>
> >>-	dev->clk = devm_clk_get(&pdev->dev, NULL);
> >>-	dev->get_clk_rate_khz = i2c_dw_get_clk_rate_khz;
> >>-	if (IS_ERR(dev->clk))
> >>-		return PTR_ERR(dev->clk);
> 
> Actually, if we don't provide the clock (which is the case for ACPI), this
> would also return and cause the probing to fail.

Indeed it seems that when you have CONFIG_COMMON_CLK selected the clock
framework starts returning errors if the clock is not found.

Since we need the clock for Intel LPSS I2C host controllers (and they
may have *CNT methods), I think you just need to provide the clock for
AMD I2C host controller in similar way than we do in
drivers/acpi/acpi_lpss.c.
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