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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 71999C4338F for ; Mon, 16 Aug 2021 05:18:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B3F661884 for ; Mon, 16 Aug 2021 05:18:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233001AbhHPFTJ (ORCPT ); Mon, 16 Aug 2021 01:19:09 -0400 Received: from ni.piap.pl ([195.187.100.5]:32894 "EHLO ni.piap.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229523AbhHPFTJ (ORCPT ); Mon, 16 Aug 2021 01:19:09 -0400 Received: from t19.piap.pl (OSB1819.piap.pl [10.0.9.19]) by ni.piap.pl (Postfix) with ESMTPSA id 17D8CC3F2A57; Mon, 16 Aug 2021 07:18:34 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 ni.piap.pl 17D8CC3F2A57 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=piap.pl; s=mail; t=1629091114; bh=2echCi4pjmtL2m5KAuC5Qg92knY9kIQM3wV9qOzNp0o=; h=From:To:Cc:Subject:References:Date:In-Reply-To:From; b=EDOypOD/p7sMjPuKr0+ODenT/LCdLqpkh6j+Hi9E79XkdR2lOK6yD8hTByS8UXyjM 6eJsKElo47zjNzrGoysd6auffOIZoxs6ZFAj2S0ld8TB21+RCWzRlRwx4t9uvlJfAW uEU1mEgrpMjFpGQpT2EKAa1VT8K6r9Wl/ROdyi98= From: =?utf-8?Q?Krzysztof_Ha=C5=82asa?= To: Bjorn Helgaas Cc: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Bjorn Helgaas , linux-pci@vger.kernel.org, Artem Lapkin , Neil Armstrong , Huacai Chen , Rob Herring , Lorenzo Pieralisi , Richard Zhu , Lucas Stach , linux-kernel@vger.kernel.org Subject: Re: [PATCH] PCIe: limit Max Read Request Size on i.MX to 512 bytes References: <20210813192254.GA2604116@bjorn-Precision-5520> Sender: khalasa@piap.pl Date: Mon, 16 Aug 2021 07:18:33 +0200 In-Reply-To: <20210813192254.GA2604116@bjorn-Precision-5520> (Bjorn Helgaas's message of "Fri, 13 Aug 2021 14:22:54 -0500") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-KLMS-Rule-ID: 1 X-KLMS-Message-Action: clean X-KLMS-AntiSpam-Lua-Profiles: 165565 [Aug 16 2021] X-KLMS-AntiSpam-Version: 5.9.20.0 X-KLMS-AntiSpam-Envelope-From: khalasa@piap.pl X-KLMS-AntiSpam-Rate: 0 X-KLMS-AntiSpam-Status: not_detected X-KLMS-AntiSpam-Method: none X-KLMS-AntiSpam-Auth: dkim=pass header.d=piap.pl X-KLMS-AntiSpam-Info: LuaCore: 454 454 39c6e442fd417993330528e7f9d13ac1bf7fdf8c, {Tracking_Text_ENG_RU_Has_Extended_Latin_Letters, eng}, {Tracking_marketers, three}, {Tracking_from_domain_doesnt_match_to}, piap.pl:7.1.1;d41d8cd98f00b204e9800998ecf8427e.com:7.1.1;t19.piap.pl:7.1.1;127.0.0.199:7.1.2 X-MS-Exchange-Organization-SCL: -1 X-KLMS-AntiSpam-Interceptor-Info: scan successful X-KLMS-AntiPhishing: Clean, bases: 2021/08/16 04:40:00 X-KLMS-AntiVirus: Kaspersky Security for Linux Mail Server, version 8.0.3.30, bases: 2021/08/15 23:54:00 #17042267 X-KLMS-AntiVirus-Status: Clean, skipped Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Bjorn Helgaas writes: >> TBH I don't think of this as of a "quirk" - all systems have MRRS >> limits, it just happens that these ones have their limit lower than 4096 >> bytes. This isn't a limitation of a particular PCIe device, this is a >> common limit of the whole system. > > Do you have a reference for this? I don't see anything in the PCIe > spec that suggests platforms must limit MRRS, and it seems that only > these ARM-related controllers have this issue. I meant there is always a limit - isn't Max_Read_Request_Size a limit? Device Control Register (Offset 08h) Bit Location 14:12 Max_Read_Request_Size allows for max 4096 bytes, though two values are reserved, so there is room for some easy extension. - non-ARM (non-DWC?) systems are limited to 4096 bytes - DWC-based systems are limited to 128, 256, 512 bytes (are there 4096-byte ones?) That's how I understand it, please correct me if I'm wrong. --=20 Krzysztof "Chris" Ha=C5=82asa Sie=C4=87 Badawcza =C5=81ukasiewicz Przemys=C5=82owy Instytut Automatyki i Pomiar=C3=B3w PIAP Al. Jerozolimskie 202, 02-486 Warszawa