From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4D02E20FABB; Fri, 10 Jan 2025 14:54:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736520863; cv=none; b=gGTWX4/uE6G07VCk+Lx0aQFGLCPWfSyJvKzyYEJIwBLhPzH9j4ROAdNoFS7ZUnSNJKlVXyarEWE4hy7vZ8RMJd9uyqCekhumYvqvr/ozkqd3BwUc4AGjtQ8ADet7kc2zuM1DleReyM0A44bAqGLpKIzib+eDIlYvRfYkSb17Ays= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736520863; c=relaxed/simple; bh=lUzSCn1AX4r6Yodul88XZtMxwiaf8Z9eTarKJqacgVY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dEB1TVoZvNR/YNTwCq7YgQiKcHgZYdCjxl20tt/B0pNbRH0kCZhAIwUH8Ml0gjxAEM+/rkKAlRonNnfi+MkZADBi6+vgaGttcgn8tyvMPSLFOwQ5mRop+VOq92crLAOORx1trB7pRIBez7r1t4ALVJHFm4rWrFTxqBiL4jnl8Zc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=c0pxdOzS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="c0pxdOzS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4779DC4CED6; Fri, 10 Jan 2025 14:54:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1736520862; bh=lUzSCn1AX4r6Yodul88XZtMxwiaf8Z9eTarKJqacgVY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=c0pxdOzSVH5CdvyZargE+BVCNBJdPGCmCGBLxTGveYLMcnFm/304SbTNmUDDqZ0Wt 82PgzbuopSXdKSI+g/ENH5BO7ZDMVwyKxt0YMRKUMXU5rhZskO64YoFW60cEenME3f qqEts4DILAuhR6df6ZRk4V5euDbWyBvfkL4pAnF4= Date: Fri, 10 Jan 2025 15:54:19 +0100 From: 'Greg Kroah-Hartman' To: "Toshiyuki Sato (Fujitsu)" Cc: Russell King , Jiri Slaby , "linux-kernel@vger.kernel.org" , "linux-serial@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] serial: amba-pl011: Implement nbcon console Message-ID: <2025011031-lying-spirits-e326@gregkh> References: <20250108004730.2302996-1-fj6611ie@aa.jp.fujitsu.com> <2025010845-deceiver-imaginary-ea04@gregkh> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Jan 09, 2025 at 01:04:36AM +0000, Toshiyuki Sato (Fujitsu) wrote: > Hi, Greg. Thanks for the comment. > > > On Wed, Jan 08, 2025 at 12:47:30AM +0000, Toshiyuki Sato wrote: > > > Implement the callbacks required for an NBCON console [0] on the > > > amba-pl011 console driver. > > > The codes for legacy console are retained, and the module > > > parameter (use_nbcon) allows switching between legacy and NBCON. > > > The default is off (use legacy console) for now. > > > > > > Referred to the NBCON implementation work for 8250 [1] and imx [2]. > > > > > > The normal-priority write_thread checks for console ownership > > > each time a character is printed. > > > write_atomic holds the console ownership until the entire string > > > is printed. > > > > > > UART register operations are protected from other contexts by > > > uart_port_lock, except for a final flush(nbcon_atomic_flush_unsafe) > > > on panic. > > > > > > The patch has been verified to correctly handle the output and > > > competition of messages with different priorities and flushing > > > panic message to console after nmi panic using ARM64 QEMU and > > > a physical machine(A64FX). > > > > > > [0] https://lore.kernel.org/all/ZuRRTbapH0DCj334@pathway.suse.cz/ > > > [1] > > https://lore.kernel.org/all/20240913140538.221708-1-john.ogness@linutronix.d > > e/T/ > > > [2] > > https://lore.kernel.org/linux-arm-kernel/20240913-serial-imx-nbcon-v3-1-4c62 > > 7302335b@geanix.com/T/ > > > > > > Signed-off-by: Toshiyuki Sato > > > --- > > > drivers/tty/serial/amba-pl011.c | 113 > > ++++++++++++++++++++++++++++++++ > > > 1 file changed, 113 insertions(+) > > > > > > diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c > > > index 69b7a3e1e..52fab3170 100644 > > > --- a/drivers/tty/serial/amba-pl011.c > > > +++ b/drivers/tty/serial/amba-pl011.c > > > @@ -41,6 +41,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > #define UART_NR 14 > > > > > > @@ -263,6 +264,7 @@ struct uart_amba_port { > > > char type[12]; > > > bool rs485_tx_started; > > > unsigned int rs485_tx_drain_interval; /* usecs */ > > > + bool console_line_ended; > > > #ifdef CONFIG_DMA_ENGINE > > > /* DMA stuff */ > > > unsigned int dmacr; /* dma control reg */ > > > @@ -274,6 +276,10 @@ struct uart_amba_port { > > > #endif > > > }; > > > > > > +/* if non-zero, the console is nbcon. */ > > > +static int use_nbcon; > > > +module_param(use_nbcon, int, 0444); > > > > Why is a module parameter needed here? That feels wrong and not > > scalable at all. What happens if you have multiple devices, which one > > is nbcon and which isn't? > > This module parameter is for pl011 driver. Yes, and module parameters are from the 1990's, let's not add new ones please. > With this patch implemented, only one type will be usable, depending > on the value of use_nbcon. > I thought it would be more user-friendly if legacy operation could be > selected via boot parameter. > Would it be better to make the patch purely nbcon-compatible, without > retaining the legacy functionality? Why would you want the "legacy" functionality? Aren't we converting all consoles over to use the new stuff? thanks, greg k-h