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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 95A06C433DF for ; Fri, 5 Jun 2020 11:34:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 79CFF207D3 for ; Fri, 5 Jun 2020 11:34:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726343AbgFELel (ORCPT ); Fri, 5 Jun 2020 07:34:41 -0400 Received: from foss.arm.com ([217.140.110.172]:53940 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbgFELel (ORCPT ); Fri, 5 Jun 2020 07:34:41 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 38EEA2B; Fri, 5 Jun 2020 04:34:40 -0700 (PDT) Received: from [10.57.10.23] (unknown [10.57.10.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 739DB3F52E; Fri, 5 Jun 2020 04:34:37 -0700 (PDT) Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support To: Florian Fainelli , linux-kernel@vger.kernel.org Cc: "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Scott Branden , lukas@wunner.de, Ray Jui , Rob Herring , "open list:SPI SUBSYSTEM" , Mark Brown , "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." , "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , Martin Sperl , Nicolas Saenz Julienne References: <20200604212819.715-1-f.fainelli@gmail.com> From: Robin Murphy Message-ID: <142d48ae-2725-1368-3e11-658449662371@arm.com> Date: Fri, 5 Jun 2020 12:34:36 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200604212819.715-1-f.fainelli@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-06-04 22:28, Florian Fainelli wrote: > The 4 SPI controller instances added in BCM2711 and BCM7211 SoCs (SPI3, > SPI4, SPI5 and SPI6) share the same interrupt line with SPI0. > > For the BCM2835 case which is deemed performance critical, we would like > to continue using an interrupt handler which does not have the extra > comparison on BCM2835_SPI_CS_INTR. FWIW, if I'm reading the patch correctly, then with sensible codegen that "overhead" should amount to a bit test on a live register plus a not-taken conditional branch - according to the 1176 TRM that should add up to a whopping 2 cycles. If that's really significant then I'd have to wonder whether you want to be at the mercy of the whole generic IRQ stack at all, and should perhaps consider using FIQ instead. > To support that requirement the common interrupt handling code between > the shared and non-shared interrupt paths is split into a > bcm2835_spi_interrupt_common() and both bcm2835_spi_interrupt() as well > as bcm2835_spi_shared_interrupt() make use of it. > > During probe, we determine if there is at least another instance of this > SPI controller, and if there is, then we install a shared interrupt > handler. > > Signed-off-by: Florian Fainelli > --- > Changes in v2: > > - identify other available SPI nodes to determine if we need to set-up > interrupt sharing. This needs to happen for the very first instance > since we cannot know for the first instance whether interrupt sharing > is needed or not. > > drivers/spi/spi-bcm2835.c | 61 ++++++++++++++++++++++++++++++++------- > 1 file changed, 50 insertions(+), 11 deletions(-) > > diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c > index 237bd306c268..0288b5b3de1e 100644 > --- a/drivers/spi/spi-bcm2835.c > +++ b/drivers/spi/spi-bcm2835.c > @@ -361,11 +361,10 @@ static void bcm2835_spi_reset_hw(struct spi_controller *ctlr) > bcm2835_wr(bs, BCM2835_SPI_DLEN, 0); > } > > -static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) > +static inline irqreturn_t bcm2835_spi_interrupt_common(struct spi_controller *ctlr, > + u32 cs) > { > - struct spi_controller *ctlr = dev_id; > struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); > - u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); > > /* > * An interrupt is signaled either if DONE is set (TX FIFO empty) > @@ -394,6 +393,27 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) > return IRQ_HANDLED; > } > > +static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) > +{ > + struct spi_controller *ctlr = dev_id; > + struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); > + u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); > + > + return bcm2835_spi_interrupt_common(ctlr, cs); > +} > + > +static irqreturn_t bcm2835_spi_shared_interrupt(int irq, void *dev_id) > +{ > + struct spi_controller *ctlr = dev_id; > + struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); > + u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); > + > + if (!(cs & BCM2835_SPI_CS_INTR)) > + return IRQ_NONE; > + > + return bcm2835_spi_interrupt_common(ctlr, cs); > +} > + > static int bcm2835_spi_transfer_one_irq(struct spi_controller *ctlr, > struct spi_device *spi, > struct spi_transfer *tfr, > @@ -1287,12 +1307,37 @@ static int bcm2835_spi_setup(struct spi_device *spi) > return 0; > } > > +static const struct of_device_id bcm2835_spi_match[] = { > + { .compatible = "brcm,bcm2835-spi", }, > + {} > +}; > +MODULE_DEVICE_TABLE(of, bcm2835_spi_match); > + > static int bcm2835_spi_probe(struct platform_device *pdev) > { > + irq_handler_t bcm2835_spi_isr_func = bcm2835_spi_interrupt; > struct spi_controller *ctlr; > + unsigned long flags = 0; > + struct device_node *dn; > struct bcm2835_spi *bs; > int err; > > + /* On BCM2711 there can be multiple SPI controllers enabled sharing the > + * same interrupt line, but we also want to minimize the overhead if > + * there is no need to support interrupt sharing. If we find at least > + * another available instane (not counting the one we are probed from), > + * then we assume that interrupt sharing is necessary. > + */ > + for_each_compatible_node(dn, NULL, bcm2835_spi_match[0].compatible) { > + err = of_device_is_available(dn) && dn != pdev->dev.of_node; > + of_node_put(dn); This is in the wrong place - it should only be where you terminate the loop early and thus bypass the "of_node_put(from)" call in the iterator itself. > + if (err) { > + flags = IRQF_SHARED; Is there really any harm to setting IRQF_SHARED even when the interrupt isn't shared in hardware? Sure, it means you lose a degree of API-level validation and some other driver might also be able to simultaneously claim it on bcm283x, but in that case the DT would be wrong and *something* isn't going to work correctly anyway, so does this one driver really need to care about trying to be the DT police? Robin. > + bcm2835_spi_isr_func = bcm2835_spi_shared_interrupt; > + break; > + } > + } > + > ctlr = spi_alloc_master(&pdev->dev, ALIGN(sizeof(*bs), > dma_get_cache_alignment())); > if (!ctlr) > @@ -1344,8 +1389,8 @@ static int bcm2835_spi_probe(struct platform_device *pdev) > bcm2835_wr(bs, BCM2835_SPI_CS, > BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX); > > - err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_interrupt, 0, > - dev_name(&pdev->dev), ctlr); > + err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_isr_func, > + flags, dev_name(&pdev->dev), ctlr); > if (err) { > dev_err(&pdev->dev, "could not request IRQ: %d\n", err); > goto out_dma_release; > @@ -1400,12 +1445,6 @@ static void bcm2835_spi_shutdown(struct platform_device *pdev) > dev_err(&pdev->dev, "failed to shutdown\n"); > } > > -static const struct of_device_id bcm2835_spi_match[] = { > - { .compatible = "brcm,bcm2835-spi", }, > - {} > -}; > -MODULE_DEVICE_TABLE(of, bcm2835_spi_match); > - > static struct platform_driver bcm2835_spi_driver = { > .driver = { > .name = DRV_NAME, >