add information about cirrusdrm driver and Linux Cirrus driver

openbsd_drm_howto.tex

@@ -7,7 +7,7 @@
 
 %opening
 \title{OpenBSD DRM/KMS driver implementation guide}
-\author{Léo Grange}
+\author{Léo Grange \\ \href{mailto:grangeleo@gmail.com}{grangeleo@gmail.com}}
 
 \bibliographystyle{plain}
 
@@ -41,12 +41,22 @@ I could do, I will try to give you as much reference as possible, and to fill th
 holes I encountered myself.
 
 As explaining abstract things with a concrete example often helps to understand,
-we will use the OpenBSD Cirrus DRM driver for illustration purpose.
-The old Cirrus chipsets are significantly easier to program than their today's
-equivalents (Intel or AMD/ATI cards).
+we will use the OpenBSD Cirrus DRM driver\footnotemark for illustration purpose.
+This driver was originally written as part of a Google Summer of Code 2015 project,
+to provide an understandable basis for future DRM drivers.
+Indeed, the old Cirrus chipsets are significantly easier to program than their
+today's equivalents (Intel or AMD/ATI cards).
 In addition, the Cirrus CL-GD5446 card is well emulated in QEMU, which makes it
 easier to test the driver and to experiment with it.
-% talk about Cirrus driver
+
+\footnotetext{
+Until \texttt{cirrusdrm} driver integration to upstream OpenBSD,
+a version of the driver is available through a git repository, at
+\url{http://lab.knightsofnii.com/kristaba/openbsd.git}, on the branch
+\texttt{cirrusdrm-current}.
+A web interface is also provided at
+\url{http://lab.knightsofnii.com/kristaba/openbsd/tree/cirrusdrm-current/sys/dev/pci/drm/cirrus}.
+}
 \end{abstract}
 
 
@@ -83,7 +93,7 @@ vice versa.
 
 % TODO explain the need of userland X.Org drivers
 
-\subsection{Userland API}
+%\subsection{Userland API}
 % TODO
 
 \subsection{Kernel driver model}
@@ -187,10 +197,16 @@ Despite the relatively well furnished documentation available on the DRM interna
 APIs, it's difficult to create a new driver without some examples.
 The example used here is \texttt{cirrusdrm}, a pretty simple driver which supports
 mainly the Cirrus CL-GD5446 chipset.
+This driver was written from scratch, based on \texttt{radeon} and \texttt{i915}
+DRM driver sources as well as the X.org DDX driver \texttt{xf86-video-cirrus}.
+A similar driver, designed to work only with the QEMU and Xen implementations of
+this chipset, exists in upstream Linux kernel for a while.
+Unfortunately, the GPL-only license of the driver prevents it to be ported to
+OpenBSD's kernel, and its authors didn't seem to agree for changing the license.
+
 As explained above, this chipset has the huge advantage to be emulated in some
-virtual machines and hypervisors (QEMU or Xen for example), resulting in an ease
+virtual machines and hypervisors (QEMU or Xen for instance), resulting in an ease
 of testing and experimenting with it.
-
 As it's a graphics card from the 90's, it has the other advantage to expose a
 pretty simple hardware, with only one CRTC, a single VGA connector and little
 acceleration capability.
@@ -1034,7 +1050,7 @@ gives an approximation of the connector helper \texttt{.mode\_valid}.
 Some modes are invalidated later, both in X.org and KMS drivers, for instance
 when memory is insufficient for a mode.
 
-
+\pagebreak
 \bibliography{openbsd-biblio}