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=-16.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 3945BC433F5 for ; Fri, 3 Sep 2021 09:31:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1102E61074 for ; Fri, 3 Sep 2021 09:31:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348856AbhICJcM (ORCPT ); Fri, 3 Sep 2021 05:32:12 -0400 Received: from foss.arm.com ([217.140.110.172]:39636 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348834AbhICJcJ (ORCPT ); Fri, 3 Sep 2021 05:32:09 -0400 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 D1E5B1FB; Fri, 3 Sep 2021 02:31:09 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B18ED3F694; Fri, 3 Sep 2021 02:31:08 -0700 (PDT) Subject: Re: [PATCH] drm/panfrost: Calculate lock region size correctly To: Boris Brezillon Cc: Rob Herring , Tomeu Vizoso , Alyssa Rosenzweig , Daniel Vetter , David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20210902140038.221437-1-steven.price@arm.com> <20210903105122.76471f98@collabora.com> From: Steven Price Message-ID: <3ba07c72-2ec8-1b2d-e089-3d8b0eb25d73@arm.com> Date: Fri, 3 Sep 2021 10:31:07 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210903105122.76471f98@collabora.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/09/2021 09:51, Boris Brezillon wrote: > On Thu, 2 Sep 2021 15:00:38 +0100 > Steven Price wrote: > >> It turns out that when locking a region, the region must be a naturally >> aligned power of 2. The upshot of this is that if the desired region >> crosses a 'large boundary' the region size must be increased >> significantly to ensure that the locked region completely covers the >> desired region. Previous calculations (including in kbase for the >> proprietary driver) failed to take this into account. >> >> Since it's known that the lock region must be naturally aligned we can >> compute the required size by looking at the highest bit position which >> changes between the start/end of the lock region (subtracting 1 from the >> end because the end address is exclusive). The start address is then >> aligned based on the size (this is technically unnecessary as the >> hardware will ignore these bits, but the spec advises to do this "to >> avoid confusion"). >> >> Signed-off-by: Steven Price >> --- >> See previous discussion[1] for more details. This bug also existed in >> the 'kbase' driver, so it's unlikely to actually hit very often. >> >> This patch is based on drm-misc-next-fixes as it builds on top of >> Alyssa's changes to lock_region. >> >> [1] https://lore.kernel.org/dri-devel/6fe675c4-d22b-22da-ba3c-f6d33419b9ed@arm.com/ >> >> drivers/gpu/drm/panfrost/panfrost_mmu.c | 33 +++++++++++++++++++------ >> 1 file changed, 26 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c >> index dfe5f1d29763..afec15bb3db5 100644 >> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c >> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c >> @@ -58,17 +58,36 @@ static int write_cmd(struct panfrost_device *pfdev, u32 as_nr, u32 cmd) >> } >> >> static void lock_region(struct panfrost_device *pfdev, u32 as_nr, >> - u64 iova, u64 size) >> + u64 region_start, u64 size) >> { >> u8 region_width; >> - u64 region = iova & PAGE_MASK; >> + u64 region; >> + u64 region_size; >> + u64 region_end = region_start + size; >> >> - /* The size is encoded as ceil(log2) minus(1), which may be calculated >> - * with fls. The size must be clamped to hardware bounds. >> + if (!size) >> + return; >> + >> + /* >> + * The locked region is a naturally aligned power of 2 block encoded as >> + * log2 minus(1). >> + * Calculate the desired start/end and look for the highest bit which >> + * differs. The smallest naturally aligned block must include this bit >> + * change the desired region starts with this bit (and subsequent bits) >> + * zeroed and ends with the bit (and subsequent bits) set to one. >> + * > > Nit: you can drop the empty comment line. Whoops - I reordered this comment and didn't spot the blank line getting left. >> */ >> - size = max_t(u64, size, AS_LOCK_REGION_MIN_SIZE); >> - region_width = fls64(size - 1) - 1; >> - region |= region_width; >> + region_size = region_start ^ (region_end - 1); > > Hm, is region_size really encoding the size of the region to lock? I > mean, the logic seems correct but I wonder if it wouldn't be better to > drop the region_size variable and inline > 'region_start ^ (region_end - 1)' in the region_width calculation to > avoid confusion. Yeah I wasn't happy about the variable name either, but I couldn't think of a better one. Inlining it into the following line nicely avoids the problem ;) > Looks good otherwise. > > Reviewed-by: Boris Brezillon Thanks, I'll post a v2 in case anyone else has other comments. Steve >> + region_width = max(fls64(region_size), >> + const_ilog2(AS_LOCK_REGION_MIN_SIZE)) - 1; >> + >> + /* >> + * Mask off the low bits of region_start (which would be ignored by >> + * the hardware anyway) >> + */ >> + region_start &= GENMASK_ULL(63, region_width); >> + >> + region = region_width | region_start; >> >> /* Lock the region that needs to be updated */ >> mmu_write(pfdev, AS_LOCKADDR_LO(as_nr), region & 0xFFFFFFFFUL); >