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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3EB7FCE8D4D for ; Fri, 14 Nov 2025 16:11:08 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vJwMu-0006Ut-Ob; Fri, 14 Nov 2025 11:09:49 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vJwJa-0005OD-3H for qemu-devel@nongnu.org; Fri, 14 Nov 2025 11:06:34 -0500 Received: from pc232-55.mailgun.net ([143.55.232.55]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1vJwJW-0004S6-D7 for qemu-devel@nongnu.org; Fri, 14 Nov 2025 11:06:20 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mail.yodel.dev; q=dns/txt; s=pdk1; t=1763136362; x=1763143562; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: From: From: References: Cc: To: To: Subject: Subject: MIME-Version: Date: Message-ID: Sender: Sender; bh=JMWv7SnNk9uHTSK+5UUAcAtgxk3r3DIoAzn0QcNOEso=; b=4aooKRYWz2tK4X2O2l5lHIJ/l71sy7RtE187a/kUZESXE+HGPRsScci1FYNN6rKRL0EzlfUoXm5hUZgHbJ2nA/gJUmMMfOlT8PivxoPbp7ySRwFQrZrriHagAJJSwKicmnHobeyPyzClS6DOMlc0WWinQG13HBmXmw6RwHoBpxNTfTmxWdjiG5bJLCBPCnZjAh71b0Dl8b4NuBbgl62h+GWOqTKmkmp4FNawYOE26vnUFMovIsg6ORx/U6U9Rk4EST+fXIgjGjpHzUwP2srYbs5z67CWslZvOss2il7FmiL23pONvSEMG+o1+RO8q8s773RKd32dgbHsU0b4u4EUaA== X-Mailgun-Sid: WyJjZmM4NiIsInFlbXUtZGV2ZWxAbm9uZ251Lm9yZyIsIjMzZTkyMCJd Received: from mail.yodel.dev (mail.yodel.dev [35.209.39.246]) by 3b7d14ad9ad78b1c6e6d7409de447049a6855f48b903eaec24781089ed31cc57 with SMTP id 69175369c093f57552b734e6; Fri, 14 Nov 2025 16:06:01 GMT X-Mailgun-Sending-Ip: 143.55.232.55 Message-ID: <4d6d7e9d-0952-4158-9ef4-6093a16e9dd9@yodel.dev> Date: Fri, 14 Nov 2025 10:05:58 -0600 MIME-Version: 1.0 Subject: Re: [RFC PATCH] hw/dma: don't allow weird transfer lengths for bcm2835 To: =?UTF-8?Q?Alex_Benn=C3=A9e?= , qemu-devel@nongnu.org Cc: Peter Maydell , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Fabiano Rosas , Laurent Vivier , Paolo Bonzini , "open list:Raspberry Pi" , Yodel Eldar References: <20251111105429.3993300-1-alex.bennee@linaro.org> Content-Language: en-US From: Yodel Eldar Autocrypt: addr=yodel.eldar@yodel.dev; keydata= xjMEZxqXdhYJKwYBBAHaRw8BAQdAkletQdG3CLyANZyuf2t7Z9PK4b6HiT+DdSPUB2mHzmPN I1lvZGVsIEVsZGFyIDx5b2RlbC5lbGRhckB5b2RlbC5kZXY+wpkEExYKAEECGwMFCQOcG00F CwkIBwIGFQoJCAsCBBYCAwECHgECF4AWIQTTzRjNQG27imap+N+V7k+3NmVNrAUCaNWASwIZ AQAKCRCV7k+3NmVNrNnSAPoDjQXa6v7ZzdQSaLdRfAQy/5SsUucv+zp3WAP4pXdgJQEAzMMC Ctx4l6b13Fs2hZdRXEnF/4BZ9t1K68nwzZOV3QnOOARnGpd2EgorBgEEAZdVAQUBAQdAKPIy 3W/DKFsm1e+31zoqmOY0pqz8vjIM846wM6lEY2QDAQgHwn4EGBYIACYCGwwWIQTTzRjNQG27 imap+N+V7k+3NmVNrAUCaNWG7QUJA5wi9wAKCRCV7k+3NmVNrPusAQCQDQwETy7VT6UhHPho TkrQnsNqQfFU3tXqCTiViToktQD7B/U2/to97hQIJCWbK6yd3T+KPZJPMcHMg2XRyedUvgA= In-Reply-To: <20251111105429.3993300-1-alex.bennee@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=143.55.232.55; envelope-from=bounce+c033f0.33e920-qemu-devel=nongnu.org@mail.yodel.dev; helo=pc232-55.mailgun.net X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 11/11/2025 04:54, Alex Bennée wrote: > The datasheet doesn't explicitly say that TXFR_LEN has to be word > aligned but the fact there is a DMA_D_WIDTH flag to select between 32 > bit and 128 bit strongly implies that is how it works. The downstream At the bottom of page 38, the datasheet [1] states "the DMA can deal with byte aligned transfers and will minimise bus traffic by buffering and packing misaligned accesses." IIUC, the *_WIDTH info fields are implied as maxima. [1] https://datasheets.raspberrypi.com/bcm2835/bcm2835-peripherals.pdf Regards, Yodel > rpi kernel also goes to efforts to not write sub-4 byte lengths so > lets: