From mboxrd@z Thu Jan 1 00:00:00 1970 From: zhichang.yuan02@gmail.com (zhichang) Date: Thu, 8 Sep 2016 18:04:31 +0800 Subject: [PATCH V2 4/4] ARM64 LPC: support earlycon for UART connected to LPC In-Reply-To: <4291379.IHAA72aKCk@wuerfel> References: <1473255233-154297-1-git-send-email-yuanzhichang@hisilicon.com> <1473255233-154297-5-git-send-email-yuanzhichang@hisilicon.com> <4291379.IHAA72aKCk@wuerfel> Message-ID: <57D137AF.9070306@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi, Arnd, On 2016?09?07? 22:52, Arnd Bergmann wrote: > On Wednesday, September 7, 2016 9:33:53 PM CEST Zhichang Yuan wrote: >> From: "zhichang.yuan" >> >> This patch support the earlycon for UART connected to LPC on Hip06. >> This patch is depended on the LPC driver. >> >> Signed-off-by: zhichang.yuan >> > > I'm skeptical about this too. Is this just needed because the 8250 > earlycon support comes before the lpc bus initialization? I think you wonder why early_serial8250_setup can not be used direclty for this earlycon of LPC uart. 1. the earlycon kernel parameter format of LPC uart is different from 8250. something like that "earlycon=hisilpcuart,mmio,0xa01b0000,0,0x2f8". You see, there is one more parameter after the baudrate. Hip06 LPC uart need two base addresses for earlycon. 2. the IO type is mmio to introduce a memory base address to access LPC register file. But the real uart IO type is UPIO_PORT. This is spcial... 3. Just as your guess, earlycon should be earlier than lpc initialization. Best, Zhichang > > Could we start the LPC driver earlier to work around that? > > Arnd >