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[50.47.106.83]) by smtp.gmail.com with ESMTPSA id 17sm647234pgy.53.2021.01.05.20.01.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jan 2021 20:01:05 -0800 (PST) Message-ID: <84e09e65b831ba6d3017a6ca9be039005b24e793.camel@gmail.com> Subject: Re: [PATCH 1/2] drm/hyperv: Add DRM driver for hyperv synthetic video device From: Deepak Rawat To: Thomas Zimmermann , Gerd Hoffmann Cc: linux-hyperv@vger.kernel.org, Wei Hu , Tang Shaofeng , Haiyang Zhang , Dexuan Cui , dri-devel@lists.freedesktop.org, Michael Kelley , Sam Ravnborg Date: Tue, 05 Jan 2021 20:01:04 -0800 In-Reply-To: <8ff4bd88-6e98-3db5-232d-98ce2c370cd1@suse.de> References: <20210102060336.832866-1-drawat.floss@gmail.com> <2b49fcd2-38f7-dae5-2992-721a8bd142a2@suse.de> <4f7818f99734c0912325e1f3b6b80cb2a04df3ef.camel@gmail.com> <20210105110438.zhy22zzqfgbnonos@sirius.home.kraxel.org> <8ff4bd88-6e98-3db5-232d-98ce2c370cd1@suse.de> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Tue, 2021-01-05 at 12:30 +0100, Thomas Zimmermann wrote: > Hi > > Am 05.01.21 um 12:04 schrieb Gerd Hoffmann: > >    Hi, > > > > > > It's not possible to do page flip with this virtual device. The > > > > call to > > > > SYNTHVID_VRAM_LOCATION is only honoured once. So unfortunately > > > > need to > > > > use SHMEM helpers. > > > > > > I was thinking about using struct > > > video_output_situation.vram_offset; in > > > case you want to tinker with that. There's a comment in the patch > > > that > > > vram_offset should always be 0. But this comment seems incorrect > > > for devices > > > with more than one output. > > > > Where does the comment come from?  fbdev drivers support a single > > framebuffer only so for a fbdev driver it makes sense to set the > > offset > > to 0 unconditionally.  With drm you probably can handle things > > differently ... > > I cannot find it in hyperv_fb.c; it must have gotten introduced here. > > Only one display is supported by this DRM driver, so the comment is > correct. In the future, having support for multiple displays might be > an > option. > > Beside that offset should be 0, another problem is that SYNTHVID_SITUATION_UPDATE will cause the whole screen to flicker (I suppose this call is more for changing resolution), so can't really use this for page-flip.