linux-kernel - Re: [PATCH v4 43/45] media: sun6i-csi: Detect the availability of the ISP

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Message-ID: <Ymp98LBQySvpz8/j@aptenodytes>
Date:   Thu, 28 Apr 2022 13:43:44 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Jernej Škrabec <jernej.skrabec@...il.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 43/45] media: sun6i-csi: Detect the availability of
 the ISP

Hi Maxime,

On Thu 28 Apr 22, 10:11, Maxime Ripard wrote:
> On Thu, Apr 28, 2022 at 09:55:56AM +0200, Paul Kocialkowski wrote:
> > Hi Jernej,
> > 
> > Thanks a lot for all your reviews!
> > 
> > On Wed 27 Apr 22, 22:07, Jernej Škrabec wrote:
> > > Dne petek, 15. april 2022 ob 17:28:09 CEST je Paul Kocialkowski napisal(a):
> > > > Add a helper to detect whether the ISP is available and connected
> > > > and store the indication in a driver-wide variable.
> > > > 
> > > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > > > ---
> > > >  .../platform/sunxi/sun6i-csi/sun6i_csi.c      | 33 +++++++++++++++++++
> > > >  .../platform/sunxi/sun6i-csi/sun6i_csi.h      |  3 ++
> > > >  2 files changed, 36 insertions(+)
> > > > 
> > > > diff --git a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > > b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c index
> > > > a88deb8ba1e7..f185cbd113c7 100644
> > > > --- a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > > +++ b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > > @@ -25,6 +25,35 @@
> > > >  #include "sun6i_csi_capture.h"
> > > >  #include "sun6i_csi_reg.h"
> > > > 
> > > > +/* ISP */
> > > > +
> > > > +static bool sun6i_csi_isp_detect(struct sun6i_csi_device *csi_dev)
> > > > +{
> > > > +	struct device *dev = csi_dev->dev;
> > > > +	struct fwnode_handle *handle = NULL;
> > > > +
> > > > +	/* ISP is not available if disabled in kernel config. */
> > > > +	if (!IS_ENABLED(CONFIG_VIDEO_SUN6I_ISP))
> > > 
> > > Where is this symbol defined?
> > 
> > That is defined through Kconfig's auto-generated header, from the associated
> > option for the ISP driver. It is defined in the ISP support series so this
> > will effectively always be false for now.
> 
> Can the ISP be compiled as a module, but the CSI driver built-in?

I think so yes, I don't see any reason why not.

> If so,
> that would create a dependency from the kernel image to a module, which
> won't compile.

I think this would introduce a run-time dependency (sun6i-csi needing sun6i-isp
in order to register) but I don't understand why it wouldn't compile though.
Could you ellaborate a bit?

Thanks!

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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