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Date: Wed, 22 May 2024 12:03:37 +0000
From: Sakari Ailus <sakari.ailus@linux.intel.com>
To: Hans de Goede <hdegoede@redhat.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Dan Carpenter <dan.carpenter@linaro.org>,
	Bingbu Cao <bingbu.cao@intel.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Daniel Scally <dan.scally@ideasonboard.com>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel-janitors@vger.kernel.org
Subject: Re: [PATCH v2] media: ipu-bridge: fix error code in ipu_bridge_init()
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In-Reply-To: <d2d71851-691f-45cf-9d52-1d16ede09b2b@redhat.com>

Hi Hans,

On Tue, May 14, 2024 at 05:38:45PM +0200, Hans de Goede wrote:
> Hi,
> 
> On 5/14/24 5:21 PM, Andy Shevchenko wrote:
> > On Tue, May 14, 2024 at 02:33:31PM +0000, Sakari Ailus wrote:
> >> On Fri, May 10, 2024 at 06:43:31PM +0300, Dan Carpenter wrote:
> > 
> > ...
> > 
> >> Neither IPU3-CIO2 or IPU6 ISYS drivers should be of any functional use
> >> without sensors. But the power states of the devices could be affected by
> >> this: the drivers should power off these devices but without drivers they
> >> maybe left powered on. I haven't made any measurements though.
> > 
> > FWIW, Hans mentioned AtomISPv2 case with somewhat 7W consumption on top of
> > the idling machine. That's why we have a stub driver in PDx86 exactly for
> > the purpose of turning it off when not used.
> 
> I'm not sure if I ever mentioned the 7W, that seems a lot. But in
> the atomisp case the SoC will never reach S0i3 when the ISP is not
> properly turned off. And in this case the ISP is special and just letting
> PCI / ACPI put it in D3 is not enough it needs some special writes on
> the IO-Sideband-Fabric to be turned off.
> 
> I don't know if something similar applies to the IPU3 / IPU6, but
> the bridge code is used by the atomisp code now too. So at a minimum
> if an error gets returned when there are no sensors then this must be unique
> enough that the atomisp code can check for it. Maybe -ENODEV ?

-ENODEV is also used for a number of different conditions. Different error
codes are also returned by functions the ipu bridge calls and they seem to
be passed onwards as-is mostly.

Maybe add an argument to ipu_bridge_init() to tell whether to fail if there
are no sensors?

-- 
Regards,

Sakari Ailus