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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 783A0C71153 for ; Tue, 29 Aug 2023 15:37:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=toJwG1rTzwhLUhsL0SAUwNuqzj7axaXBg48H5J8s8Ys=; b=Z4lv+EAE6qn4py hi92Z+ibYe/j128i7Jen2HUqkUUtNw70tWQq1Q1I0itWz4gJJytQUjQKwLn1Ir4QkdmZaIerbjp2O fxmKIlkMZ9pOnhs5X3xo4Jnhc/BVd4OUnY0GrMOJGckV6z6P0sRABNI9ppwocyb8VkJpTtqoaCEGl VqvMjg2+BbQayuod9SwMJTXOhx/Lz204jQ9aZJTfJb4lSHu11bf9SbvBn8AT5NAN/uEr7gsed9q7s ul1cu8KJGvPtcjOaPgp5jtDaoPHv85F26tmmQv3LYplUj7tJY9bSaPH7ofYeGUvmJ/M1k53XmZg9B 8EbV9T/gV97p7PJNgBRg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qb0mI-00BnOa-39; Tue, 29 Aug 2023 15:37:15 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qb0mG-00BnNo-0p for linux-arm-kernel@lists.infradead.org; Tue, 29 Aug 2023 15:37:13 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6A2472F4; Tue, 29 Aug 2023 08:37:45 -0700 (PDT) Received: from [10.1.34.35] (010265703453.arm.com [10.1.34.35]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A68AF3F738; Tue, 29 Aug 2023 08:37:04 -0700 (PDT) Message-ID: <61f9b371-7c45-26b1-ec0f-600765280c89@arm.com> Date: Tue, 29 Aug 2023 16:37:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Thunderbird/102.14.0 Subject: Re: [PATCH 1/3] iommu/io-pgtable-arm: Add nents_per_pgtable in struct io_pgtable_cfg Content-Language: en-GB To: Nicolin Chen Cc: will@kernel.org, jgg@nvidia.com, joro@8bytes.org, jean-philippe@linaro.org, apopple@nvidia.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev References: <0fe68babdb3a07adf024ed471fead4e3eb7e703f.1692693557.git.nicolinc@nvidia.com> From: Robin Murphy In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230829_083712_361378_69E35492 X-CRM114-Status: GOOD ( 13.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2023-08-22 17:42, Nicolin Chen wrote: > On Tue, Aug 22, 2023 at 10:19:21AM +0100, Robin Murphy wrote: > >>> out_free_data: >>> @@ -1071,6 +1073,7 @@ arm_mali_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie) >>> ARM_MALI_LPAE_TTBR_ADRMODE_TABLE; >>> if (cfg->coherent_walk) >>> cfg->arm_mali_lpae_cfg.transtab |= ARM_MALI_LPAE_TTBR_SHARE_OUTER; >>> + cfg->nents_per_pgtable = 1 << data->bits_per_level; >> >> The result of this highly complex and expensive calculation is clearly >> redundant with the existing bits_per_level field, so why do we need to >> waste space storing when the driver could simply use bits_per_level? > > bits_per_level is in the private struct arm_lpae_io_pgtable, while > drivers can only access struct io_pgtable_cfg. Are you suggesting > to move bits_per_level out of the private struct arm_lpae_io_pgtable > to the public struct io_pgtable_cfg? > > Or am I missing another bits_per_level? Bleh, apologies, I always confuse myself trying to remember the fiddly design of io-pgtable data. However, I think this then ends up proving the opposite point - the number of pages per table only happens to be a fixed constant for certain formats like LPAE, but does not necessarily generalise. For instance for a single v7s config it would be 1024 or 256 or 16 depending on what has actually been unmapped. The mechanism as proposed implicitly assumes LPAE format, so I still think we're better off making that assumption explicit. And at that point arm-smmu-v3 can then freely admit it already knows the number is simply 1/8th of the domain page size. Thanks, Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel