From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Date: Wed, 28 Jan 2015 10:37:14 +0100 Subject: [U-Boot] [PATCH 4/4] sunxi: video: Force h/vsync active high when using ext. vga dac In-Reply-To: <1422436425.29309.31.camel@hellion.org.uk> References: <1422196540-18093-1-git-send-email-hdegoede@redhat.com> <1422196540-18093-4-git-send-email-hdegoede@redhat.com> <1422436425.29309.31.camel@hellion.org.uk> Message-ID: <54C8ADCA.6080001@redhat.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi, On 28-01-15 10:13, Ian Campbell wrote: > On Sun, 2015-01-25 at 15:35 +0100, Hans de Goede wrote: >> On both my A13-OLinuxIno and my A13-OLinuxIno-Micro, the vga output gives an >> unstable image when active low v or hsync is used, so when an external vga dac >> is used force v and hsync active high independent of what the modeline says. > > Does this not just mean the modeline is wrong and should be fixed or an > alternative provided which is correct for these systems? I would rather not, the modeline uses is a vesa standard timing, so it certainly is correct. The problem seems to be specific with the OLinuxIno A13 (normal & micro) boards. I've just looked up the schematics and they use an opendrain driver for the vga sync lines, and with sync pulses it is the logical high->low edge of the pulse which counts for the timing, which with an active low sync is being driven by the pull-up, and that simply seems to not drive it hard enough to get a stable image. > In the code comment you say "some dacs", what about ones which don't > have this issue or, worse, ones which have the inverse issue and don't > work with active high? > > At the least I'd say this aught to be controllable via Kconfig. I agree this should be a Kconfig and only turned on on the Olinuxino 13 boards. I'll do a v2. Regards, Hans