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smtp.gmail.com with ESMTPSA id n2sm13483757pgn.71.2020.01.26.12.20.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 26 Jan 2020 12:20:39 -0800 (PST) Subject: Re: [PATCH] serial: 8250_early: Add earlycon for BCM2835 aux uart To: Lukas Wunner , matthias.bgg@kernel.org Cc: gregkh@linuxfoundation.org, jslaby@suse.com, nsaenzjulienne@suse.de, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Matthias Brugger , Florian Fainelli , Ray Jui , Scott Branden , Stephen Boyd , bcm-kernel-feedback-list@broadcom.com References: <20200126123314.3558-1-matthias.bgg@kernel.org> <20200126131238.c65zj3wo3srafa7z@wunner.de> From: Matthias Brugger Autocrypt: addr=matthias.bgg@gmail.com; prefer-encrypt=mutual; keydata= mQINBFP1zgUBEAC21D6hk7//0kOmsUrE3eZ55kjc9DmFPKIz6l4NggqwQjBNRHIMh04BbCMY fL3eT7ZsYV5nur7zctmJ+vbszoOASXUpfq8M+S5hU2w7sBaVk5rpH9yW8CUWz2+ZpQXPJcFa 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NMDbxcY26CMPK204jhRm9RG687qq6691hbiuAtWABeAsl1AS+mdS7aP/4uOM4kFCvXYgIHxP /BoVz9CZTMEVAZVzbRKyYCLUf1wLhcHzugTiONz9fWMBLLskKvq7m1tlr61mNgY9nVwwClMU uE7i1H9r/2/UXLd+pY82zcXhFrfmKuCDmOkB5xPsOMVQJH8I0/lbqfLAqfsxSb/X1VKaP243 jzi+DzD9cvj2K6eD5j5kcKJJQactXqfJvF1Eb+OnxlB1BCLE8D1rNkPO5O742Mq3MgDmq19l +abzEL6QDAAxn9md8KwrA3RtucNh87cHlDXfUBKa7SRvBjTczDg+HEPNk2u3hrz1j3l2rliQ y1UfYx7Vk/TrdwUIJgKS8QAr8Lw9WuvY2hSqL9vEjx8VAkPWNWPwrQ== Message-ID: <88af0fca-90d1-58ff-406d-73f185eb8b7e@gmail.com> Date: Sun, 26 Jan 2020 21:20:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200126131238.c65zj3wo3srafa7z@wunner.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/01/2020 14:12, Lukas Wunner wrote: > On Sun, Jan 26, 2020 at 01:33:14PM +0100, matthias.bgg@kernel.org wrote: >> +#ifdef CONFIG_SERIAL_8250_CONSOLE >> + >> +static int __init early_bcm2835aux_setup(struct earlycon_device *device, >> + const char *options) >> +{ >> + if (!device->port.membase) >> + return -ENODEV; >> + >> + device->port.iotype = UPIO_MEM32; >> + device->port.regshift = 2; >> + >> + return early_serial8250_setup(device, NULL); >> +} >> + >> +OF_EARLYCON_DECLARE(bcm2835aux, "brcm,bcm2835-aux-uart", >> + early_bcm2835aux_setup); >> +#endif > > Does this really work? I also tried to get it working recently and > the system just hung on boot. Looking at it with a JTAG debugger > showed that the bcm2835aux registers were inaccessible because > the mini UART wasn't enabled in the AUXENB register. > > Maybe if you use OF_EARLYCON_DECLARE, the firmware recognizes that > serial1 is set as stdout-path and performs enablement of the mini UART? > Or are you using U-Boot which perhaps does the enablement? Yes I'm using U-Boot which enables the console for me. My understanding is that the early console is thought as a re-use of the console the boot FW used for logging. AFAIK for example it does not enable any needed clocks but expects these to be enabled already. Looking on the source code of U-Boot [1] I don't see that the AUXENB is written somewhere, so I suppose that the FW should already has enabled the aux-uart. I any case if it's just to set one bit, I think we can do that in early_bcm2835aux_setup(). [1] https://gitlab.denx.de/u-boot/u-boot/blob/master/drivers/serial/serial_bcm283x_mu.c > > I also saw in the JTAG debugger that the uartclk member contained > an incorrect value, so I'd expect that it has to be set as well in > early_bcm2835aux_setup(). In my case the clock was set by U-Boot already. Regards, Matthias > > I'll see to it that I give this patch a whirl when I return to the > office next week. > > Thanks, > > Lukas >