linux-kernel - Re: [PATCH 3/5] i2c: designware: add MSCC Ocelot support

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Date:   Tue, 17 Jul 2018 15:19:08 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        James Hogan <jhogan@...nel.org>
Cc:     Paul Burton <paul.burton@...s.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Allan Nielsen <allan.nielsen@...rosemi.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH 3/5] i2c: designware: add MSCC Ocelot support

On Tue, 2018-07-17 at 13:48 +0200, Alexandre Belloni wrote:
> The Microsemi Ocelot I2C controller is a designware IP. It also has a
> second set of registers to allow tweaking SDA hold time and spike
> filtering.

Can you elaborate a bit?

Are they platform specific? Are they shadow registers? Are they
something else? Datasheet link / excerpt would be also good to read.
 
>  Optional properties :
> + - reg : for "mscc,ocelot-i2c", a second register set to configure
> the SDA hold
> +   time, named ICPU_CFG:TWI_DELAY in the datasheet.
> +

Hmm... Is this registers unique to the SoC in question? Is address of
them fixed or may be configured on RTL level?

If former is right, why do we need a separate property?

>  
> +#define MSCC_ICPU_CFG_TWI_DELAY		0x0
> +#define MSCC_ICPU_CFG_TWI_DELAY_ENABLE	BIT(0)
> +#define MSCC_ICPU_CFG_TWI_SPIKE_FILTER	0x4
> +
> +static int mscc_twi_set_sda_hold_time(struct dw_i2c_dev *dev)
> +{
> +	writel((dev->sda_hold_time << 1) |
> MSCC_ICPU_CFG_TWI_DELAY_ENABLE,
> +	       dev->base_ext + MSCC_ICPU_CFG_TWI_DELAY);
> +
> +	return 0;
> +}

Hmm... And does how this make native DesignWare IP's registers obsolete?


> +	if (of_device_is_compatible(pdev->dev.of_node, "mscc,ocelot-
> i2c"))

Can't you just ask for this unconditionally? Why not?
(It seems I might have known why not, but can we use named resource
instead in case this is not so SoC specific)


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