From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 988F5C433F5 for ; Fri, 11 Feb 2022 10:20:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242036AbiBKKU1 (ORCPT ); Fri, 11 Feb 2022 05:20:27 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:49502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229671AbiBKKUZ (ORCPT ); Fri, 11 Feb 2022 05:20:25 -0500 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 146F82A5; Fri, 11 Feb 2022 02:20:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1644574823; x=1676110823; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=RJ+0ZmlVTd1NI8J1ND1o+WTJfa5qruEZ7EtRTsDra1o=; b=nbCIxheDepA12YuGBuiLfifyx6PXQOa49hfOofMdqt6bI4D44jGHmDQI wlgpDGiXK13XFEw1qidcsCmSnbI63f/3iikT4b91xpgnY/G4039m0OlpQ hsKxRmNIm31f93u/xWrTg/Ccamg/2SO9awkF41q0lRRwzkGhRSx9TSost q69Pj/V4/HQwDOtigVUYAG2rvbYVHTkjTgg28r5LPsiiz5Xk9maZ+HjTZ cLBg9SSBCAg1xSFvdLfazTJdsEBHfYIsFKxDwv/jqwdJJZVHDt6MepHGJ QMattY31J7bAU27APUgpgKQwLleGdOhWj4u/oYE9A1VGMtQAvmvGLxHwc w==; X-IronPort-AV: E=McAfee;i="6200,9189,10254"; a="248538209" X-IronPort-AV: E=Sophos;i="5.88,360,1635231600"; d="scan'208";a="248538209" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Feb 2022 02:20:13 -0800 X-IronPort-AV: E=Sophos;i="5.88,360,1635231600"; d="scan'208";a="568999001" Received: from smile.fi.intel.com ([10.237.72.61]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Feb 2022 02:20:10 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.95) (envelope-from ) id 1nIT1F-003PAX-4u; Fri, 11 Feb 2022 12:19:13 +0200 Date: Fri, 11 Feb 2022 12:19:12 +0200 From: Andy Shevchenko To: Zev Weiss Cc: Greg Kroah-Hartman , Joel Stanley , Andrew Jeffery , Jiri Slaby , Konstantin Aladyshev , Oskar Senft , openbmc@lists.ozlabs.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type Message-ID: References: <20220211004203.14915-1-zev@bewilderbeest.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220211004203.14915-1-zev@bewilderbeest.net> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 10, 2022 at 04:42:03PM -0800, Zev Weiss wrote: > Commit 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to > set up register mapping") fixed a bug that had, as a side-effect, > prevented the 8250_aspeed_vuart driver from enabling the VUART's > FIFOs. However, fixing that (and hence enabling the FIFOs) has in > turn revealed what appears to be a hardware bug in the ASPEED VUART in > which the host-side THRE bit doesn't get if the BMC-side receive FIFO > trigger level is set to anything but one byte. This causes problems > for polled-mode writes from the host -- for example, Linux kernel > console writes proceed at a glacial pace (less than 100 bytes per > second) because the write path waits for a 10ms timeout to expire > after every character instead of being able to continue on to the next > character upon seeing THRE asserted. (GRUB behaves similarly.) > > As a workaround, introduce a new port type for the ASPEED VUART that's > identical to PORT_16550A as it had previously been using, but with > UART_FCR_R_TRIG_00 instead to set the receive FIFO trigger level to > one byte, which (experimentally) seems to avoid the problematic THRE > behavior. ... > + [PORT_ASPEED_VUART] = { > + .name = "ASPEED VUART", > + .fifo_size = 16, > + .tx_loadsz = 16, > + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00, > + .rxtrig_bytes = {1, 4, 8, 14}, > + .flags = UART_CAP_FIFO, > + }, This is quite similar to AR7 type. Can that be (re-)used? -- With Best Regards, Andy Shevchenko