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[217.229.16.64]) by smtp.gmail.com with ESMTPSA id c38sm3914634edb.15.2018.12.11.02.00.33 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 11 Dec 2018 02:00:33 -0800 (PST) Date: Tue, 11 Dec 2018 11:00:32 +0100 From: Thierry Reding To: Hans Verkuil Cc: Hans Verkuil , Mauro Carvalho Chehab , Jonathan Hunter , linux-media@vger.kernel.org, linux-tegra@vger.kernel.org Subject: Re: [PATCH 1/2] media: tegra-cec: Support Tegra186 and Tegra194 Message-ID: <20181211100032.GC14426@ulmo> References: <20181210160038.16122-1-thierry.reding@gmail.com> <643e8da6-a8ed-145a-604d-f028e501add9@xs4all.nl> <20181210205945.GB325@mithrandir> <96df2b5f-e388-b933-8823-c718290bd5e3@xs4all.nl> <20181211093807.GA14426@ulmo> <26035940-2364-1fa0-68ab-8b9327705eb4@xs4all.nl> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ctP54qlpMx3WjD+/" Content-Disposition: inline In-Reply-To: <26035940-2364-1fa0-68ab-8b9327705eb4@xs4all.nl> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org --ctP54qlpMx3WjD+/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Dec 11, 2018 at 10:40:55AM +0100, Hans Verkuil wrote: > (Resend, this time with a proper reply) >=20 > On 12/11/18 10:38 AM, Thierry Reding wrote: > > On Tue, Dec 11, 2018 at 10:19:48AM +0100, Hans Verkuil wrote: > >> On 12/10/18 9:59 PM, Thierry Reding wrote: > >>> On Mon, Dec 10, 2018 at 06:07:10PM +0100, Hans Verkuil wrote: > >>>> Hi Thierry, > >>>> > >>>> On 12/10/18 5:00 PM, Thierry Reding wrote: > >>>>> From: Thierry Reding > >>>>> > >>>>> The CEC controller found on Tegra186 and Tegra194 is the same as on > >>>>> earlier generations. > >>>> > >>>> Well... at least for the Tegra186 there is a problem that needs to b= e addressed first. > >>>> No idea if this was solved for the Tegra194, it might be present the= re as well. > >>>> > >>>> The Tegra186 hardware connected the CEC lines of both HDMI outputs t= ogether. This is > >>>> a HW bug, and it means that only one of the two HDMI outputs can use= the CEC block. > >>> > >>> I don't know where you got that information from, but I can't find any > >>> indication of that in the documentation. My understanding is that the= re > >>> is a single CEC block that is completely independent and it is merely= a > >>> decision of the board designer where to connect it. I'm not aware of = any > >>> boards that expose more than a single CEC. > >> > >> Sorry, my memory was not completely correct. > >> > >> The problem is that the 186 can be configured with two HDMI outputs, b= ut it has > >> only one CEC block. So CEC can be used for only one of the two. I chec= ked the TRM > >> for the Tegra194 and that has up to four HDMI outputs, but still only = one CEC > >> block. > >> > >> And yes, it is the responsibility for the board designer to hook up th= e CEC pin > >> to only one of the outputs, but the TRM never explicitly mentions this= and given > >> the general lack of knowledge about CEC it wouldn't surprise me at all= if there > >> will be wrong board designs. > >> > >> But be that as it may, the core problem remains: you cannot allow mult= iple > >> HDMI outputs to be connected to the same CEC device. > >> > >> However, I now realize that your patches will actually work fine since= each > >> HDMI connector tries to get a cec notifier for its own HDMI device, bu= t the > >> tegra-cec driver will only register a notifier for the HDMI device poi= nted > >> to by the hdmi-phandle property. So only one of the HDMI devices will = actually > >> get a working CEC. > >> > >> Although if board designers mess this up and connect multiple CEC line= s to > >> the same CEC pin, this would still break, but there is nothing that ca= n be > >> done about that. I still believe the TRM should have made this clear s= ince > >> it is not obvious. Even better would be to have the same number of CEC= blocks > >> as there are configurable HDMI outputs. Typically, if you support CEC = on one > >> HDMI output, you want to support it for all. And today that's not poss= ible > >> without adding external CEC devices (as we - Cisco - do). > >=20 > > I wasn't aware that anyone was using a Tegra with support for multiple > > HDMI outputs. Do you have a contact that you can forward this kind of > > request to? It certainly sounds like something that would be useful to > > add in future chips if there's a customer need. >=20 > We have contacts, and we did report it, but nothing happened with it > AFAIK. It was likely too late for changes to the Tegra194 design in any > case. Okay. I'll follow up internally, see if I can find out what the story is. 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