From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Gupta, Pekon" Subject: RE: [PATCH 1/3] spi/qspi: Add memory mapped read support. Date: Tue, 15 Oct 2013 18:33:23 +0000 Message-ID: <20980858CB6D3A4BAE95CA194937D5E73EA23640@DBDE04.ent.ti.com> References: <52566ACC.1080100@ti.com> <20131010101410.GG21581@sirena.org.uk> <52568AA3.9080203@ti.com> <20131011100839.GA21581@sirena.org.uk> <525CDB77.4040201@ti.com> <20131015111647.GX2443@sirena.org.uk> <525D2BB3.4020705@ti.com> <20131015124656.GM2443@sirena.org.uk> <525D41E2.30206@ti.com> <20131015180142.GS23337@ld-irv-0074.broadcom.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Peter Korsgaard , "Balbi, Felipe" , Mark Brown , "linux-mtd@lists.infradead.org" , "spi-devel-general@lists.sourceforge.net" , "Poddar, Sourav" , Brian Norris , David Woodhouse To: Trent Piepho Return-path: In-Reply-To: Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-mtd" Errors-To: linux-mtd-bounces+gldm-linux-mtd-36=gmane.org@lists.infradead.org List-Id: linux-spi.vger.kernel.org > From: Trent Piepho > Are there any numbers to show if memory mapped read support is a > benefit in Linux? There is some question as to whether it's useful at > all or not. > > If it is, I think low latency for small reads is probably one of the > only advantages. To do that, you aren't going to want to deal with > device PM for every single read. It would make more sense to turn the > hardware on when the MTD device is opened and leave it on until > closed. > +1 Therefore early suggestions were to make 'MM_MODE' as default (if device enables it via DT). This means: (1) switch to 'SPI_MODE' _only_ when required for commands like mtd_erase, etc. and switch back to 'MM_MODE' when done. (2) And keep your controller clocks on. This would ensure that you do minimum config-switching when using MM_MODE. And would thus achieve low latency, and no driver intervention. Yes, real thruput numbers would help clear the picture here .. with regards, pekon ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/ From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from comal.ext.ti.com ([198.47.26.152]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1VW9Rv-00010i-T4 for linux-mtd@lists.infradead.org; Tue, 15 Oct 2013 18:34:32 +0000 From: "Gupta, Pekon" To: Trent Piepho Subject: RE: [PATCH 1/3] spi/qspi: Add memory mapped read support. Date: Tue, 15 Oct 2013 18:33:23 +0000 Message-ID: <20980858CB6D3A4BAE95CA194937D5E73EA23640@DBDE04.ent.ti.com> References: <52566ACC.1080100@ti.com> <20131010101410.GG21581@sirena.org.uk> <52568AA3.9080203@ti.com> <20131011100839.GA21581@sirena.org.uk> <525CDB77.4040201@ti.com> <20131015111647.GX2443@sirena.org.uk> <525D2BB3.4020705@ti.com> <20131015124656.GM2443@sirena.org.uk> <525D41E2.30206@ti.com> <20131015180142.GS23337@ld-irv-0074.broadcom.com> In-Reply-To: Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: Peter Korsgaard , "Balbi, Felipe" , Mark Brown , "linux-mtd@lists.infradead.org" , "spi-devel-general@lists.sourceforge.net" , "Poddar, Sourav" , Brian Norris , David Woodhouse List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > From: Trent Piepho > Are there any numbers to show if memory mapped read support is a > benefit in Linux? There is some question as to whether it's useful at > all or not. >=20 > If it is, I think low latency for small reads is probably one of the > only advantages. To do that, you aren't going to want to deal with > device PM for every single read. It would make more sense to turn the > hardware on when the MTD device is opened and leave it on until > closed. >=20 +1 Therefore early suggestions were to make 'MM_MODE' as default (if device enables it via DT). This means: (1) switch to 'SPI_MODE' _only_ when required for commands like mtd_erase, etc. and switch back to 'MM_MODE' when done. (2) And keep your controller clocks on. This would ensure that you do minimum config-switching when using MM_MODE. And would thus achieve low latency, and no driver intervention. Yes, real thruput numbers would help clear the picture here .. with regards, pekon