From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thierry Reding Subject: Re: [RFC 3/6] dt/bindings: Add bindings for Tegra20/30 NOR bus driver Date: Tue, 26 Jul 2016 10:32:40 +0200 Message-ID: <20160726083240.GA2433@ulmo.ba.sec> References: <1468935397-11926-1-git-send-email-mirza.krak@gmail.com> <1468935397-11926-4-git-send-email-mirza.krak@gmail.com> <20160725113034.GD21170@ulmo.ba.sec> <20160725141544.GN21170@ulmo.ba.sec> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="fdj2RfSjLxBAspz7" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Mirza Krak Cc: Stephen Warren , Alexandre Courbot , pdeschrijver-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, Prashant Gaikwad , Michael Turquette , sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, pawel.moll-5wv7dgnIgG8@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org, Kumar Gala , linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org List-Id: devicetree@vger.kernel.org --fdj2RfSjLxBAspz7 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jul 25, 2016 at 09:59:34PM +0200, Mirza Krak wrote: > 2016-07-25 16:15 GMT+02:00 Thierry Reding : > > On Mon, Jul 25, 2016 at 03:16:28PM +0200, Mirza Krak wrote: > >> 2016-07-25 13:30 GMT+02:00 Thierry Reding : > >> > > >> > I would've expected this to require some sort of infrastructure to a= llow > >> > devices connected to the GMI controller to acquire the bus via some = API > >> > to select their chip. > >> > >> Yes, ultimately you would need some sort of infrastructure to allow > >> devices to acquire the GMI bus if you want to solve this in software. > >> But at the moment I do not see such an infrastructure in place, and is > >> it feasible to add one specifically for the GMI controller? If one > >> such infrastructure was in place we would need to modify all the > >> drivers that want to use to include Tegra specific infrastructure to > >> access the GMI bus? > >> > >> Since my knowledge is limited it hard for me to comment on this, maybe > >> there is a simple way of doing this? > > > > I don't think there's a simple way to do this. In order to properly > > implement it we'd need to implement a generic infrastructure for chip > > selects so that drivers such as the one for your CAN controller can be > > written without tying them specifically to the Tegra GMI controller. > > > > From what you and Jon were saying it sounds like the drivers are > > completely agnostic of any chip-select, so conversion won't be easy. > > But technically if these chips take a chip-select as input then it's > > always possible to hook them up to a controller that doesn't do this > > automatic translation of address to chip-select, so eventually some > > setup is bound to come along where they'd need explicit chip-select > > handling as well. > > > > I don't think it's fair to require you to implement this infrastructure > > if you don't actually need it. At the same time I want to be cautious > > and make sure we keep the driver and binding flexible enough to allow > > us to implement explicit chip-selects should we later need them. > > > > Thierry >=20 > One thing that should be noted, and that is the GMI controller also > supports a DMA master mode (feature for the future?). >=20 > I do not really know how this effects the binding we are discussing > but wanted to put it out there. Yes, that had occurred to me as well. I don't really have any good ideas on how to use that other than to implement it as a DMA engine driver and have drivers use those, if available. But I don't think we have to worry about it right now. If we ever need it, the binding can be extended in a backwards-compatible way. 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