Re: [PATCH RFC 18/18] ARM: dts: Add minimal Raspberry Pi 4 support

From: Stefan Wahren <stefan.wahren@i2se.com>
To: Marc Zyngier <marc.zyngier@arm.com>, Stefan Wahren <wahrenst@gmx.net>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Scott Branden <sbranden@broadcom.com>,
	Stephen Boyd <sboyd@kernel.org>, Ray Jui <rjui@broadcom.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Eric Anholt <eric@anholt.net>, Rob Herring <robh+dt@kernel.org>,
	bcm-kernel-feedback-list@broadcom.com,
	Mark Brown <broonie@kernel.org>,
	Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
	Michael Turquette <mturquette@baylibre.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-rpi-kernel@lists.infradead.org
Subject: Re: [PATCH RFC 18/18] ARM: dts: Add minimal Raspberry Pi 4 support
Date: Sun, 28 Jul 2019 12:58:58 +0200	[thread overview]
Message-ID: <ebcb934d-7bab-bfc7-3371-1b5032b67ec7@i2se.com> (raw)
In-Reply-To: <20190723191326.3afdff83@why>

Hi Marc,

Am 23.07.19 um 20:13 schrieb Marc Zyngier:
> On Wed, 17 Jul 2019 23:16:04 +0200
> Stefan Wahren <wahrenst@gmx.net> 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 <wahrenst@gmx.net>
>>
>> ...
>> +	};
>> +
>> +	timer {
>> +		compatible = "arm,armv7-timer";
>> +		interrupts = <GIC_PPI 13 (GIC_CPU_MASK_SIMPLE(4) |
>> +					  IRQ_TYPE_LEVEL_LOW)>,
>> +			     <GIC_PPI 14 (GIC_CPU_MASK_SIMPLE(4) |
>> +					  IRQ_TYPE_LEVEL_LOW)>,
>> +			     <GIC_PPI 11 (GIC_CPU_MASK_SIMPLE(4) |
>> +					  IRQ_TYPE_LEVEL_LOW)>,
>> +			     <GIC_PPI 10 (GIC_CPU_MASK_SIMPLE(4) |
>> +					  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.
>
>> +		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.

Stefan

[1] - https://github.com/raspberrypi/linux/issues/3101
[2] - https://github.com/raspberrypi/tools/blob/master/armstubs/armstub8.S

>
> Thanks,
>
> 	M.

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