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 A8A10387347; Wed, 13 May 2026 10:35:02 +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=1778668502; cv=none; b=bs+0ONbuAvgRK0PrVpSMsRLYnSVnoR0kKOODLyYkHOddaM0hPyZDmhLPndA5SdIxXKT9hu9ciAs4iZ7Y9eaSHw2wmAsHSDWEjnBLuuUOZezapsdqWj6J9n9q7m14rj/8nooSOU02RvlJHEzDS+E4yajLE81Y4QtdyI1+ce+L6V4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778668502; c=relaxed/simple; bh=vJzmSQDI+kPOU4dG6WYjc2WqLxKtDKAaNkpx0gfXFr0=; h=Date:From:To:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mvGjo4PGXC7HTIVSZVQgloVXm2hkbxKD/cEWJ76XrYNp1sEzxPY3zgng5CPvmTpRuMgh5+cVDBniuhc9JDOT+cgvP0HldAsHPu6EO68SALXY2iQwHqMU2KceSHMJCUJcc3KRxMKumxiroPKsB4HNuPYOrMfc8oLTE9XJypzmLBM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kSr94M6Y; 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="kSr94M6Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBC07C2BCB7; Wed, 13 May 2026 10:35:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1778668502; bh=vJzmSQDI+kPOU4dG6WYjc2WqLxKtDKAaNkpx0gfXFr0=; h=Date:From:To:Subject:References:In-Reply-To:From; b=kSr94M6YamK9Oud9Jk2769IHML0qw4O1sgmSzCnAUKAOR/0Tu862ZhukHAPd/XAxf 5IIOqt8BIyIvAXcsr8P0wtVNYVb5MdUkmnb0/LIBjVwoQTwiq9QChFM0+M9HfYwWyA zk4039LNrxInjph8+Z7BPJjfysXxXcQTtO5WbPCg= Date: Wed, 13 May 2026 10:48:59 +0200 From: Greg Kroah-Hartman To: Johan Hovold , Crescent Hsieh , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 4/4] usb: serial: mxuport: add sysfs control for UART FIFO Message-ID: <2026051321-apply-charting-150e@gregkh> References: <20260324035041.352190-1-crescentcy.hsieh@moxa.com> <20260324035041.352190-5-crescentcy.hsieh@moxa.com> Precedence: bulk X-Mailing-List: linux-kernel@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 Wed, May 13, 2026 at 10:20:21AM +0200, Johan Hovold wrote: > On Tue, May 12, 2026 at 07:28:19PM +0800, Crescent Hsieh wrote: > > On Thu, May 07, 2026 at 05:59:05PM +0200, Johan Hovold wrote: > > > On Tue, Mar 24, 2026 at 11:50:41AM +0800, Crescent Hsieh wrote: > > > > Add a per-port sysfs attribute, uart_fifo, to allow userspace to enable > > > > or disable the UART FIFO at runtime. > > > > > > Why would you want to do that? > > > > > > We should try to avoid driver specific sysfs knobs. > > > > The motivation is to allow userspace to choose between lower latency and > > higher throughput at runtime. Some latency-sensitive request/response > > deployments become unreliable if the UART FIFO is enabled due to the > > added buffering delay. > > Please mention this in the commit message. Wait, no one should EVER be relying on USB for latency-sensitive situations. USB does not guarantee this at all, and if you put a uart in the way, like you are doing here, that just makes it even worse and even more non-determinisitic. Please don't think that this is even a viable solution, it is not. And no papering over it in the kernel will ever give you the requirements that you need, so please do not do this. Just use a "real" uart on a PCI bus if you expect anything close to determinism. thanks, greg k-h