Re: [PATCH] i2c: designware: Round down ACPI provided clk to nearest supported clk

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, 2017-08-29 at 14:08 +0200, Hans de Goede wrote:
> The Lenovo Miix2 8 DSDT contains an i2c clk / bus speed of 1700000 Hz
> for one if its devices, which is not supported.
> 
> This is the second DSDT to show up with an unsupported clk in a short
> time, remove the hardcoded fix for DSDTs with a 1 MiHz clock and
> simply
> always round down the clk to the nearest supported value.
> 
> Reported-by: russianneuromancer@ya.ru
> Fixes: 682c6c2188 ("i2c: designware: Some broken DSTDs use 1MiHz ...")
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/i2c/busses/i2c-designware-platdrv.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c
> b/drivers/i2c/busses/i2c-designware-platdrv.c
> index 57248bccadbc..2b98a173136f 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -256,7 +256,8 @@ static int dw_i2c_plat_probe(struct
> platform_device *pdev)
>  	struct dw_i2c_dev *dev;
>  	u32 acpi_speed, ht = 0;
>  	struct resource *mem;
> -	int irq, ret;
> +	int i, irq, ret;
> +	const int supported_speeds[] = { 0, 100000, 400000, 1000000,
> 3400000 };
>  
>  	irq = platform_get_irq(pdev, 0);
>  	if (irq < 0)
> @@ -297,9 +298,16 @@ static int dw_i2c_plat_probe(struct
> platform_device *pdev)
>  	}
>  
>  	acpi_speed = i2c_acpi_find_bus_speed(&pdev->dev);
> -	/* Some broken DSTDs use 1MiHz instead of 1MHz */
> -	if (acpi_speed == 1048576)
> -		acpi_speed = 1000000;
> +	/*
> +	 * Some DSTDs use a non standard speed, round down to the
> lowest
> +	 * standard speed.
> +	 */
> +	for (i = 1; i < ARRAY_SIZE(supported_speeds); i++) {
> +		if (acpi_speed < supported_speeds[i])
> +			break;
> +	}
> +	acpi_speed = supported_speeds[i - 1];

I dunno what standard says if we may or may not use 100 kHz as a last
resort even for speeds defined less than 100 kHz.


-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy