linux-kernel - Re: [PATCH] platform/x86: Add Intel ISP dummy driver

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Date:   Wed, 29 Aug 2018 21:20:11 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Darren Hart <dvhart@...radead.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-acpi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform/x86: Add Intel ISP dummy driver

On Wed, Aug 29, 2018 at 03:57:44PM +0200, Hans de Goede wrote:
> The Image Signal Processor found on Cherry Trail devices is brought up in
> D0 state on devices which have camera sensors attached to it. The ISP will
> not enter D3 state again without some massaging of its registers beforehand
> and the ISP not being in D3 state blocks the SoC from entering S0ix modes.
> 
> There was a driver for the ISP in drivers/staging but that got removed
> again because it never worked. It does not seem likely that a real
> driver for the ISP will be added to the mainline kernel anytime soon.
> 
> This commit adds a dummy driver which contains the necessary magic from
> the staging driver to powerdown the ISP, so that Cherry Trail devices where
> the ISP is used will properly use S0ix modes when suspended.
> 
> Together with other recent S0ix related fixes this allows S0ix modes to
> be entered on e.g. a Chuwi Hi8 Pro and a HP x2 210.
> 

Thanks for the patch, my comments below.

>  drivers/platform/x86/intel_isp_dummy.c | 119 +++++++++++++++++++++++++

First of all, I would like to see that this is about pm and pm only, so,
perhaps

intel_isp_pm ?

OTOH, it would be nice to have less confusing of what ISP we are talking about,
so,

intel_atomisp2_pm ?

> +config INTEL_ISP_DUMMY
> +	tristate "Intel ISP dummy driver"

> +	depends on PCI && IOSF_MBI && PM

If someone decides to port this to kernels where ATOMISP driver is still
available, it might be a conflict here. I dunno if it's a good idea to put
something like depends !ATOMISP here taking into consideration that it would be
staled option.

> +	while (1) {

A nit: I would rather put it like

do {
...
} while (time_after(...));

> +		/* Wait until ISPSSPM0 bit[25:24] shows 0x3 */
> +		iosf_mbi_read(BT_MBI_UNIT_PMC, MBI_REG_READ, ISPSSPM0, &val);
> +		val = (val & ISPSSPM0_ISPSSS_MASK) >> ISPSSPM0_ISPSSS_OFFSET;
> +		if (val == ISPSSPM0_IUNIT_POWER_OFF)
> +			break;
> +
> +		if (time_after(jiffies, timeout)) {
> +			dev_err(&dev->dev, "IUNIT power-off timeout.\n");
> +			return -EBUSY;
> +		}
> +		usleep_range(1000, 2000);
> +	}

-- 
With Best Regards,
Andy Shevchenko