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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hsmGf-0006ct-02; Wed, 31 Jul 2019 10:55:37 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hsmGb-0006RW-LI; Wed, 31 Jul 2019 10:55:35 +0000 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 2378C337; Wed, 31 Jul 2019 03:55:29 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DBF6C3F71F; Wed, 31 Jul 2019 03:55:26 -0700 (PDT) Subject: Re: [PATCH RFC 18/18] ARM: dts: Add minimal Raspberry Pi 4 support To: Stefan Wahren , Stefan Wahren References: <1563398164-2679-1-git-send-email-wahrenst@gmx.net> <1563398164-2679-5-git-send-email-wahrenst@gmx.net> <20190723191326.3afdff83@why> <86v9vmmlsd.wl-marc.zyngier@arm.com> <6f3933b5-3b6c-f76b-3c7b-8cbf4e23108b@gmx.net> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <6f3933b5-3b6c-f76b-3c7b-8cbf4e23108b@gmx.net> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190731_035533_794447_E5CEBD34 X-CRM114-Status: GOOD ( 24.24 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Ulf Hansson , Florian Fainelli , Scott Branden , Stephen Boyd , Ray Jui , Linus Walleij , Adrian Hunter , Eric Anholt , Rob Herring , bcm-kernel-feedback-list@broadcom.com, Mark Brown , Nicolas Saenz Julienne , Michael Turquette , linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 30/07/2019 19:33, Stefan Wahren wrote: > Hi Marc, >>> Hi Marc, >>> >>> Am 23.07.19 um 20:13 schrieb Marc Zyngier: >>>> On Wed, 17 Jul 2019 23:16:04 +0200 >>>> Stefan Wahren wrote: >>>> >>>>> This adds minimal support for the new Raspberry Pi 4 without the >>>>> fancy stuff like GENET, PCIe, XHCI, 40 bit DMA and V3D. The RPi 4 is available >>>>> in 3 different variants (1, 2 and 4 GB RAM), so leave the memory size to zero >>>>> and let the bootloader take care of it. >>>>> >>>>> Other differences to the Raspberry Pi 3: >>>>> - additional GIC 400 Interrupt controller >>>>> - new thermal IP and HWRNG >>>>> - additional MMC interface (emmc2) >>>>> - additional UART, I2C, SPI and PWM interfaces >>>>> >>>>> Signed-off-by: Stefan Wahren >>>>> >>>>> ... >>>>> + }; >>>>> + >>>>> + timer { >>>>> + compatible = "arm,armv7-timer"; >> BTW, this should be "arm,armv8-timer". >> >>>>> + interrupts = >>>> + IRQ_TYPE_LEVEL_LOW)>, >>>>> + >>>> + IRQ_TYPE_LEVEL_LOW)>, >>>>> + >>>> + IRQ_TYPE_LEVEL_LOW)>, >>>>> + >>>> + IRQ_TYPE_LEVEL_LOW)>; >>>>> + arm,cpu-registers-not-fw-configured; >>>> Really? :-( >>> i asked about that [1] and they said that the arm stubs [2] only set the >>> timer frequency and zeroing CNTVOFF_EL2. >> Who is "they"? As long as it is done on all CPUs, that's the right >> thing to do, and this property is pretty useless in that case. > > "They" are the developer at Raspberry Pi Trading. I forwarded some > questions regarding this topic to them, but didn't get a reply yet. My > current understanding is that the armv8 stubs do setup the timer, but > the armv7 stubs do not. So we probably need to keep it. >From what I gather, these stubs can be updated (and apparently are updated regularly). So why not fix them once and for all? > >> >>>>> + always-on; >>>> I'm pretty sure that's not the case. This indicates that you can power >>>> the CPU off, bring it back on, and yet have your timer alive and >>>> kicking. The only case this actually exists is for VMs. I can see it >>>> being cargo-culted from previous RPi revisions, but that doesn't make >>>> it true. >>> They said that they used this to suppress high interrupt load for the >>> timers. >> Indeed, and that's the only thing the kernel can do if it isn't >> provided with a global timer that can be used as a backup then the >> CPUs transition to a deep idle state where the timers are not actually >> running. >> >> If you have such a global timer, enable it and you'll see the >> interrupt rate dropping like a rock. Don't you have a >> brcm,bcm2835-system-timer stashed somewhere? > > I've got the feedback that the system timer still exists. Unfortunately > i don't have the new interrupt definition yet. So i need to wait for > this before sending a new version of this series. Sure, no problem. I also wonder whether the SoC has the memory-mapped generic timer, which would make a lot of sense... Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel