From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA89DC433E0 for ; Fri, 12 Mar 2021 10:11:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDD0F64FC9 for ; Fri, 12 Mar 2021 10:11:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233029AbhCLKLT (ORCPT ); Fri, 12 Mar 2021 05:11:19 -0500 Received: from fllv0016.ext.ti.com ([198.47.19.142]:45762 "EHLO fllv0016.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232952AbhCLKK7 (ORCPT ); Fri, 12 Mar 2021 05:10:59 -0500 Received: from lelv0265.itg.ti.com ([10.180.67.224]) by fllv0016.ext.ti.com (8.15.2/8.15.2) with ESMTP id 12CAAeIR047426; Fri, 12 Mar 2021 04:10:40 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1615543840; bh=w9BhnOsEXmDnJr92k5Gv+KiRM15+qBMHanC1ChiW5y8=; h=Date:From:To:CC:Subject:References:In-Reply-To; b=Q1y4mXRmZoDuNdAxSGTuidk/rBcl5zVhXbMMSrben/24a6sldTbhEvz/T84eVCUD9 Zb/9ylbktvKAocZiKm3aYcervRw2AWWppoMaADkwV+bKFYfb8Db/ZbJ+5WtAgtDIX1 nSwMa/4tHCDvMbE9QUm9Fh1ITR7/Ey7tThYBVmNU= Received: from DLEE105.ent.ti.com (dlee105.ent.ti.com [157.170.170.35]) by lelv0265.itg.ti.com (8.15.2/8.15.2) with ESMTPS id 12CAAeDF039353 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Fri, 12 Mar 2021 04:10:40 -0600 Received: from DLEE103.ent.ti.com (157.170.170.33) by DLEE105.ent.ti.com (157.170.170.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Fri, 12 Mar 2021 04:10:40 -0600 Received: from fllv0040.itg.ti.com (10.64.41.20) by DLEE103.ent.ti.com (157.170.170.33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2 via Frontend Transport; Fri, 12 Mar 2021 04:10:40 -0600 Received: from localhost (ileax41-snat.itg.ti.com [10.172.224.153]) by fllv0040.itg.ti.com (8.15.2/8.15.2) with ESMTP id 12CAAdIv038442; Fri, 12 Mar 2021 04:10:39 -0600 Date: Fri, 12 Mar 2021 15:40:38 +0530 From: Pratyush Yadav To: CC: , , , , , , , , , , , , , Subject: Re: [RFC PATCH 0/6] spi: Add OSPI PHY calibration support for spi-cadence-quadspi Message-ID: <20210312101036.jfz2733ssv4nhfey@ti.com> References: <20210311191216.7363-1-p.yadav@ti.com> <9c551f56-4c00-b41a-f051-8b7e197fbcdc@microchip.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <9c551f56-4c00-b41a-f051-8b7e197fbcdc@microchip.com> User-Agent: NeoMutt/20171215 X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org On 12/03/21 09:09AM, Tudor.Ambarus@microchip.com wrote: > On 3/11/21 9:12 PM, Pratyush Yadav wrote: > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > > > Hi, > > > > This series adds support for OSPI PHY calibration on the Cadence OSPI > > controller. This calibration procedure is needed to allow high clock > > speeds in 8D-8D-8D mode. The procedure reads some pre-determined pattern > > data from the flash and runs a sequence of test reads to find out the > > optimal delays for high speed transfer. More details on the calibration > > procedure in patch 5/6. > > Can the calibration sequence be avoided if the controller is informed > about the frequency on which the flash operates? Maybe I don't understand this correctly, but there should not be any frequency on which the flash operates. The controller drives the SPI clock so the frequency is decided by the controller. Sure, there is a max supported frequency for the flash but the controller can run it slower than that if it wishes. The flash has no say in that. Anyway, the exact frequency at which the flash is running is not it is looking for. More details below. > > Can you add more details about the optimal delays? Are we talking about > flash's AC characteristics? Is the calibration still needed if the upper > layer informs the QSPI controller about the needed delays? There is usually a delay from when the flash drives the data line (IOW, puts a data bit on it) and when the signal reaches the controller. This delay can vary by the flash, board, silicon characteristics, temperature, etc. At lower speeds (25 MHz for example) this delay is not a problem because the clock period is longer so there is much more time to sample the data line. It is very likely the controller will sample at a time when the data line is valid. At high speeds (166 MHz for example), especially in DDR mode, this delay starts to play a larger role because the time to sample the data line is much smaller. Now unless the delay is accounted for, it is possible that the controller samples the data line too late or too early and sees invalid data. These delays depend on physical characteristics so it is not possible for any upper layer to inform the controller about it. How will they even know what the required delay is? In summary, no, there is no way an upper layer can inform the controller about this delay. > > Cheers, > ta > > > > > The main problem here is telling the controller where to find the > > pattern and how to read it. This RFC uses nvmem cells which point to a > > fixed partition containing the data to do the reads. It depends on [0] > > and [1]. > > > > The obvious problem with this is it won't work when the partitions are > > defined via command line. I don't see any good way to add nvmem cells to > > command line partitions. I would like some help or ideas here. We don't > > necessarily have to use nvmem either. Any way that can cleanly and > > consistently let the controller find out where the pattern is stored is > > good. > > > > The dts patch depends on [2]. > > > > Tested on TI's J721E EVM. > > > > [0] https://patchwork.ozlabs.org/project/linux-mtd/patch/20210302190012.1255-1-zajec5@gmail.com/ > > [1] https://patchwork.ozlabs.org/project/linux-mtd/patch/20210308011853.19360-1-ansuelsmth@gmail.com/ > > [2] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20210305153926.3479-2-p.yadav@ti.com/ > > > > Pratyush Yadav (6): > > spi: spi-mem: Tell controller when device is ready for calibration > > mtd: spi-nor: core: consolidate read op creation > > mtd: spi-nor: core: run calibration when initialization is done > > spi: cadence-qspi: Use PHY for DAC reads if possible > > spi: cadence-qspi: Tune PHY to allow running at higher frequencies > > arm64: dts: ti: k3-j721e-som-p0: Enable PHY calibration > > > > arch/arm64/boot/dts/ti/k3-j721e-som-p0.dtsi | 55 ++ > > drivers/mtd/spi-nor/core.c | 74 +- > > drivers/spi/spi-cadence-quadspi.c | 820 +++++++++++++++++++- > > drivers/spi/spi-mem.c | 12 + > > include/linux/spi/spi-mem.h | 8 + > > 5 files changed, 916 insertions(+), 53 deletions(-) > > > > -- > > 2.30.0 > > > > > > _______________________________________________ > > linux-arm-kernel mailing list > > linux-arm-kernel@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > > -- Regards, Pratyush Yadav Texas Instruments Inc.