From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Date: Tue, 25 Sep 2018 13:47:43 +1000 From: David Gibson Subject: Re: Portable DT Connectors with regard to FPGAs Message-ID: <20180925034743.GD30868@umbus.fritz.box> References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="BI7KTAps+wX7oIMI" Content-Disposition: inline In-Reply-To: To: Alan Tull Cc: Frank Rowand , Pantelis Antoniou , Rob Herring , Moritz Fischer , linux-fpga@vger.kernel.org, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , linux-kernel , Stephen Boyd , Mark Brown , Grant Likely List-ID: --BI7KTAps+wX7oIMI Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 24, 2018 at 03:32:44PM -0500, Alan Tull wrote: > My interest here was in having some discussion on whether connectors > are a good match for handling FPGAs. >=20 > The relevant use model is where a user applies a DT overlay targeting > an FPGA region after the kernel has booted. That overlay initiates > FPGA programming and then adds nodes for the new FPGA hardware. This > is discussed more completely in the FPGA manager DT binding document > [1]. The main deal here is that I'd like to be able to add nodes > in/below a FPGA region node to support devices in the FPGA (and be > able also to remove them if we are going to reconfigure the FPGA.) >=20 > Previous discussions about DT connectors focused on the types of > things likely to be on a physical connector. GPIO and SPI got named as > good examples for discussion while MMIO specifically was dismissed > [2]. That's problematic for embedded FPGAs for example since the FPGA > is on a mmio bus and hardware that is programmed into the FPGA lives > on that mmio bus similar to any embedded peripherals. So there's a > question - are mmio busses intended to be left un-connectorizable? I don't see any particular reason that a connector couldn't be used for mmio devices. I think you'd want to treat the connection point as a bridge on the mmio bus - that can have a 'ranges' property mapping the connected device into the parent bus's address space (as an identity mapping or otherwise). >=20 > Alan >=20 > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tr= ee/Documentation/devicetree/bindings/fpga/fpga-region.txt >=20 > [2] https://lkml.org/lkml/2016/7/20/560 >=20 --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --BI7KTAps+wX7oIMI Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEdfRlhq5hpmzETofcbDjKyiDZs5IFAlupr8oACgkQbDjKyiDZ s5K7MhAAvzTQruD8Eug/NpcLk36W4uVPasCdGxhjWNmHE0+hjEAX9OET2QK1y4OL NAlDCJAiOYr9L6ljqUSP64jtJ8RKab2LhiYzS/NXFiG8f8keCiitmJXRmCQ4DoqU 7+NEKk9GpMfmtflmUcAOqAxShwiCRdfazsP3uPHGb54zMCTioci8b7vetKydmSEu hKh1aYjD5reKcb/JfVYUPQ4k38hHCrQtzcU0VECST2nkvJOCnfvmMQn5Qa+k2aow UjMPHZnkFu1WBJRrermwQs7WWpN4Lp1pVBuM/0fThUwF12AFydr2TevWHHgOgFvC iIMFbjHIV0bbzgV+bLQ2SPhJ8YB8p+H1uBnplBCLZUFUPE7/tbEK/91wcQr4F543 e/LlWlblgJHmdlV6zgqp4ZOZ/g4JuYQsscvc5B4sajheQHJ5cLG0HSj+tKZEzRdY D7P6461froQSTBjldXGY1uP5O2GFvtebdKPYepDJN/XAHHyHpJuxlMgjZsWhEZSi 3kNLTWpuHjUAhc2tsjmCCZObj5fp3+R1KnMdbbMzUSYiQD4atN5b1e0Sc78Lt9vB 51mI4xpq/2Wkt7RojTIYN3Z1X5EVSDaZxcDz5NVrjQCOS1dnM1i6m3BgExL4UQGj idcGkHtfQH/OGrD+hk0Y3VhlzMptP5AAQrYPdRudUbnesIrjzCw= =MnJW -----END PGP SIGNATURE----- --BI7KTAps+wX7oIMI--