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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4DB64C32751 for ; Wed, 7 Aug 2019 16:45:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 25AAB2229C for ; Wed, 7 Aug 2019 16:45:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730045AbfHGQp1 (ORCPT ); Wed, 7 Aug 2019 12:45:27 -0400 Received: from mga03.intel.com ([134.134.136.65]:6866 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730036AbfHGQp1 (ORCPT ); Wed, 7 Aug 2019 12:45:27 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Aug 2019 09:36:33 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,357,1559545200"; d="scan'208";a="192946806" Received: from lahna.fi.intel.com (HELO lahna) ([10.237.72.157]) by fmsmga001.fm.intel.com with SMTP; 07 Aug 2019 09:36:29 -0700 Received: by lahna (sSMTP sendmail emulation); Wed, 07 Aug 2019 19:36:29 +0300 Date: Wed, 7 Aug 2019 19:36:29 +0300 From: 'Mika Westerberg' To: David Laight Cc: 'Yehezkel Bernat' , LKML , Andreas Noever , Michael Jamet , "Rafael J . Wysocki" , Len Brown , Lukas Wunner , Mario Limonciello , Anthony Wong , "linux-acpi@vger.kernel.org" Subject: Re: [PATCH 3/8] thunderbolt: Use 32-bit writes when writing ring producer/consumer Message-ID: <20190807163629.GV2716@lahna.fi.intel.com> References: <20190705095800.43534-1-mika.westerberg@linux.intel.com> <20190705095800.43534-4-mika.westerberg@linux.intel.com> <0f3a47d8133945b181d623ea6e0d53f2@AcuMS.aculab.com> <20190807161359.GT2716@lahna.fi.intel.com> <79616dd147864771b0b74901e77f2607@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <79616dd147864771b0b74901e77f2607@AcuMS.aculab.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Wed, Aug 07, 2019 at 04:22:26PM +0000, David Laight wrote: > From: Mika Westerberg > > Sent: 07 August 2019 17:14 > > To: David Laight > > > > On Fri, Jul 05, 2019 at 04:04:19PM +0000, David Laight wrote: > > > > Really a matter of taste, but maybe you want to consider having a single > > > > function, with a 3rd parameter, bool is_tx. > > > > The calls here will be unified to: > > > > ring_iowrite(ring, ring->head, ring->is_tx); > > > > (No condition is needed here). > > > > > > > > The implementation uses the new parameter to decide which part of the register > > > > to mask, reducing the code duplication (in my eyes): > > > > > > > > val = ioread32(ring_desc_base(ring) + 8); > > > > if (is_tx) { > > > > val &= 0x0000ffff; > > > > val |= value << 16; > > > > } else { > > > > val &= 0xffff0000; > > > > val |= value; > > > > } > > > > iowrite32(val, ring_desc_base(ring) + 8); > > > > > > > > I'm not sure if it improves the readability or makes it worse. Your call. > > > > > > Gah, that is all horrid beyond belief. > > > If a 32bit write is valid then the hardware must not be updating > > > the other 16 bits. > > > In which case the driver knows what they should be. > > > So it can do a single 32bit write of the required value. > > > > I'm not entirely sure I understand what you say above. Can you shed some > > light on this by a concrete example how it should look like? :-) > > The driver must know both the tx and rx ring values, so: > iowrite32(tx_val << 16 | rx_val, ring_desc_base(ring) + 8); > I see. However, prod or cons side gets updated by the hardware as it processes buffers and other side is only updated by the driver. I'm not sure the above works here. > The ioread32() is likely to be very slow - you only want to do them > if absolutely necessary. > The speed of the iowrite32() doesn't matter (much) since it is almost > certainly 'posted' and execution continues while the bus cycle is > in progress. OK thanks for the explanation.