From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Brown Subject: Re: [PATCH] can: mcp251x: convert to half-duplex SPI Date: Mon, 25 May 2020 12:31:06 +0100 Message-ID: <20200525113106.GB4544@sirena.org.uk> References: <1582655734-20890-1-git-send-email-tharvey@gateworks.com> <0ac77abd-0df5-e437-ea46-f6c77f59b81c@pengutronix.de> <0b351fe3-8fe9-572f-fd85-e2aed22873e3@pengutronix.de> <7b85e098-b9a9-dd14-203f-100cdf2e703e@pengutronix.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="H1spWtNR+x+ondvy" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Marc Kleine-Budde Cc: Tim Harvey , open list , linux-can@vger.kernel.org, Wolfgang Grandegger , Timo =?iso-8859-1?B?U2NobPzfbGVy?= , Andy Shevchenko , linux-spi@vger.kernel.org, Jan Glauber , Robert Richter List-Id: linux-can.vger.kernel.org --H1spWtNR+x+ondvy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 25, 2020 at 01:17:01PM +0200, Marc Kleine-Budde wrote: > On 5/21/20 10:19 PM, Tim Harvey wrote: >=20 > > Should I be submitting this patch with logic that only does > > half-duplex if the spi controller doesn't support it (if > > (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX)) or is it > > acceptable to simply make the driver half-duplex like this for all > > cases? > Please make half duplex transfers depending on SPI_CONTROLLER_HALF_DUPLEX= as > most drivers have a considerable overhead at the end of a transfer. > Most of them wait for a transfer complete interrupt. Which might take lon= ger > than the actual SPI transfer. Splitting one full duplex read-register tra= nsfer > (which is a write followed by a read) into two half duplex transfers woul= d kill > performance on full duplex capable controllers. This isn't something that every individual driver should be doing, such rewriting should happen in the core so that everything sees the benefit. --H1spWtNR+x+ondvy Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAl7LrHkACgkQJNaLcl1U h9DwqAf/V+1R+vBRqkKkyks2bM3wtNzPWu0J6yu5m72o4v1ta238UGDZ5MUZhlqF 3ofiN6ZiLfy4a5xnV3JvdhqKJ6vtqbJOFIRH/PJ854KvA1vguhUqg1Nq0mylm2Os Z9bUOhk7x5MzYEtOntpOm4E+Xx/RSTr07gxz72Lyk/9VovTdsv/3yRSalNAM47zq wSjJ5YE9nX00qw0NW1S2Ix9b97BMjhcHISFcB14kiLTTpOBQ5G77dPPDXNzNK+fV BHaMi6S2s0HtwMOnZO5c7huaGrA5a0zX2b+UognPUtZKjDSSIETXbycHFLoR+iqR zGazUbVbLveAyK65adOFXf2oJOGjRA== =802q -----END PGP SIGNATURE----- --H1spWtNR+x+ondvy--