Re: [PATCH 2/3] drm/exynos: add dt-binding documentation for rotator

[Tomasz Figa <tomasz.figa@gmail.com>]

On Monday 22 of July 2013 16:00:22 Sylwester Nawrocki wrote:
> On 07/22/2013 03:31 PM, Inki Dae wrote:
> >> ---Original Message-----
> >> 
> >> > From: linux-samsung-soc-owner@vger.kernel.org
> >> > [mailto:linux-samsung-soc- owner@vger.kernel.org] On Behalf Of
> >> > Lucas Stach
> >> > Sent: Monday, July 22, 2013 9:47 PM
> >> > To: Inki Dae
> >> > Cc: 'Mark Rutland'; 'Chanho Park';
> >> > linux-samsung-soc@vger.kernel.org;
> >> > devicetree-discuss@lists.ozlabs.org; sw0312.kim@samsung.com; dri-
> >> > devel@lists.freedesktop.org; kyungmin.park@samsung.com;
> >> > kgene.kim@samsung.com; linux-arm-kernel@lists.infradead.org
> >> > Subject: Re: [PATCH 2/3] drm/exynos: add dt-binding documentation
> >> > for
> >> > rotator
> >> > 
> >> > Am Montag, den 22.07.2013, 21:37 +0900 schrieb Inki Dae:
> >>>> > > > -----Original Message-----
> >>>> > > > From: Mark Rutland [mailto:mark.rutland@arm.com]
> >>>> > > > Sent: Monday, July 22, 2013 5:48 PM
> >>>> > > > To: Chanho Park
> >>>> > > > Cc: inki.dae@samsung.com; kgene.kim@samsung.com;
> >>>> > > > linux-samsung-
> >>>> > > > soc@vger.kernel.org; jy0922.shim@samsung.com; devicetree-
> >>>> > > > discuss@lists.ozlabs.org; sw0312.kim@samsung.com; dri-
> >>>> > > > devel@lists.freedesktop.org; kyungmin.park@samsung.com;
> >>>> > > > linux-arm-
> >>>> > > > kernel@lists.infradead.org
> >>>> > > > Subject: Re: [PATCH 2/3] drm/exynos: add dt-binding
> >>>> > > > documentation for
> >>>> > > > rotator
> >>>> > > > 
> >>>> > > > On Mon, Jul 22, 2013 at 07:49:26AM +0100, Chanho Park wrote:
> >>>>> > > > > This patch adds a dt-binding document for exynos rotator.
> >>>>> > > > > It
> >> > 
> >> > describes
> >> > 
> >>>> > > > which
> >>>> > > > 
> >>>>> > > > > nodes should be defined to use the rotator.
> >>>>> > > > > 
> >>>>> > > > > Signed-off-by: Chanho Park <chanho61.park@samsung.com>
> >>>>> > > > > Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> >>>>> > > > > ---
> >>>>> > > > > 
> >>>>> > > > >  .../bindings/drm/exynos/samsung-rotator.txt        |   35
> >>>> > > > 
> >>>> > > > ++++++++++++++++++++
> >>>> > > > 
> >>>>> > > > >  1 file changed, 35 insertions(+)
> >>>>> > > > >  create mode 100644
> >>>> > > > 
> >>>> > > > Documentation/devicetree/bindings/drm/exynos/samsung-rotator.
> >>>> > > > txt
> >>>> > > > 
> >>>>> > > > > diff --git
> >>>>> > > > > a/Documentation/devicetree/bindings/drm/exynos/samsung-
> >>>> > > > 
> >>>> > > > rotator.txt
> >>>> > > > b/Documentation/devicetree/bindings/drm/exynos/samsung-
> >>>> > > > rotator.txt
> >>>> > > > 
> >>>>> > > > > new file mode 100644
> >>>>> > > > > index 0000000..6b1d704
> >>>>> > > > > --- /dev/null
> >>>>> > > > > +++
> >>>>> > > > > b/Documentation/devicetree/bindings/drm/exynos/samsung-
> >> > 
> >> > rotator.txt
> >> > 
> >>>>> > > > > @@ -0,0 +1,35 @@
> >>>>> > > > > +* Samsung Image Rotator
> >>>>> > > > > +
> >>>>> > > > > +Required properties:
> >>>>> > > > > +  - compatible : value should be the
> >>>>> > > > > "samsung,exynos4210".
> >>> > > 
> >>> > > Please, add more compatible strings for other SoC.
> >>> > > 
> >>>>> > > > > +  - reg : Physical base address of the IP registers and
> >>>>> > > > > length of
> >>>> > > > 
> >>>> > > > memory
> >>>> > > > 
> >>>>> > > > > +	  mapped region.
> >>>>> > > > > +  - interrupts : interrupt number to the CPU.
> >>>>> > > > > +  - clocks : clock number of exynos4 rotator clock.
> >>>>> > > > > +  - clocks : clock name of rotator
> >>>> > > > 
> >>>> > > > clock-names?
> >>>> > > > 
> >>>>> > > > > +  - status : "okay" or "disabled"
> >>>>> > > > > +  - limit table for image formats :
> >>>>> > > > > min_w/min_h/max_w/max_h for
> >> > 
> >> > min/max
> >> > 
> >>>> > > > of image
> >>>> > > > 
> >>>> > > > Limit table? This doesn't seem to be a well-defined binding,
> >>>> > > > and it
> >>>> > > > seems like a relatively generic thing to describe.
> >>>> > > > 
> >>>>> > > > > +
> >>>>> > > > > +Example:
> >>>>> > > > > +	rotator: rotator@12810000 {
> >>>>> > > > > +		compatible = "samsung,exynos4210-rotator";
> >>>>> > > > > +		reg = <0x12810000 0x1000>;
> >>>>> > > > > +		interrupts = <0 83 0>;
> >>>>> > > > > +		clocks = <&clock 278>;
> >>>>> > > > > +		clock-names = "rotator";
> >>>>> > > > > +		status = "disabled";
> >>>>> > > > > +		ycbcr420_2p {
> >>>> > > > 
> >>>> > > > Which names are allowed for these subnodes?
> >>>> > > > 
> >>>>> > > > > +			min_w = <32>;
> >>>>> > > > > +			min_h = <32>;
> >>>>> > > > > +			max_w = <32768>;
> >>>>> > > > > +			max_h = <32768>;
> >>>>> > > > > +			align = <3>;
> >>>> > > > 
> >>>> > > > min-width, min-height, max-width, max-height? What units are
> >>>> > > > they in?
> >>>> > > > 
> >>>> > > > What does alignment specify exactly?
> >>>> > > > 
> >>>> > > > Are these a configurable part of the rotator hardware, or are
> >>>> > > > these
> >>>> > > > values always the same?
> >>> > > 
> >>> > > Right, that seems like configurable part. At least, min_w/h and
> >>> > > max_w/h
> >> > 
> >> > can
> >> > 
> >>> > > be different values according to SoC and pixel formats so they
> >>> > > should be described enough in this dt-binding document file.
> >> > 
> >> > Is there really this much configurability? Could each of those
> >> > values be a different on different SoCs
> > 
> > Not much but Yes. Rotator devices of Exynos SoC support various pixel
> > formats; RGB888, RGB565, YUV422, YUV420-2Plane, and YUV420-3Plane,
> > and each of these pixel formats could be different limitation to
> > minimum and maximum sizes. For example, the below shows the
> > limitation to Rotator device of Exynos4412 SoC according to pixel
> > formats,> 
> >          Image format          Minimum size          Maximum size
> >          
> >           RGB888                    8x8                     8kx8k
> >           RGB565                    16x16                  16kx16k
> >           YUV422                    16x16                  16kx16k
> >           YUV420 2-Plane         32x32                  32kx32k(in
> >           case of Y components) YUV420 3-Plane         64x32         
> >                   32kx32k(in case of Y components)> 
> > And, I guess those limitations are slightly different according to
> > Exynos SoC versions as long as I know.
> > 
> > Thanks,
> > Inki Dae
> > 
> >> > , or could you just extract those values
> >> > from the SoC/rotator hardware version and thus the DT compatible
> >> > string?
> My gut feeling is that those constraints could be well defined
> in the driver as static data and selected by the compatible property.
> Defining this in Device Tree may easily get out of control, when the
> limits become dependant on more parameters.
> 
> Whether devices should be described in much detail in DT rather than
> using multiple compatible strings had been discussed multiple times,
> for instance please see thread [1].

+1

The binding should not describe hardware functionality and how it works, 
but rather what hardware it is, unless it is really necessary. In this 
case this information can be placed in per-compatible static driver data, 
so there is no such need.

Best regards,
Tomasz