From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B82221B95B; Thu, 31 Oct 2024 21:18:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730409530; cv=none; b=CXH2mRRwXU4wNodljRDIX3MetPYWidbibuU4fLqKwLL4jfFsleNDJ2pcdn6CmJATNUIiZ0F57kYH3xBSKdaOF11QvfihoHBnP5tq7T1Q3talz9KyPor6I1nGPlAhmbYVCwJ9T+U1iTCAnPfQ0k+K5Rzr/8A5848T7u8BppVIj/M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730409530; c=relaxed/simple; bh=cpF4AAIzOXZkhcxxrsLBIFg7A1MuiEGbI4VYVNmRk2I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fXWydcTckPwAkrENjwo9kxOzW6qUXDA6oe73dDomPtcinqiaTcpbbconc0jeDRz/wewdwp0fneIXmrIlw+hPi2llObKDKN80ioNPt8PeZdq3aQOxXSSdjk7jJfQU05QxUe/Uktpo8UvWK1d3hA+q0/k1h1EGjLZB19CtjS5T3DY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 C6EFD153B; Thu, 31 Oct 2024 14:19:11 -0700 (PDT) Received: from [10.1.196.40] (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 334AF3F73B; Thu, 31 Oct 2024 14:18:30 -0700 (PDT) Message-ID: <7e362d8b-c02a-4327-9c5d-af1c4725ddc7@arm.com> Date: Thu, 31 Oct 2024 21:18:11 +0000 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 08/17] dma-mapping: add a dma_need_unmap helper To: Leon Romanovsky , Jens Axboe , Jason Gunthorpe , Joerg Roedel , Will Deacon , Christoph Hellwig , Sagi Grimberg Cc: Keith Busch , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , Marek Szyprowski , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Andrew Morton , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org References: <00385b3557fa074865d37b0ac613d2cb28bcb741.1730298502.git.leon@kernel.org> From: Robin Murphy Content-Language: en-GB In-Reply-To: <00385b3557fa074865d37b0ac613d2cb28bcb741.1730298502.git.leon@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 30/10/2024 3:12 pm, Leon Romanovsky wrote: > From: Christoph Hellwig > > Add helper that allows a driver to skip calling dma_unmap_* > if the DMA layer can guarantee that they are no-nops. > > Signed-off-by: Christoph Hellwig > Signed-off-by: Leon Romanovsky > --- > include/linux/dma-mapping.h | 5 +++++ > kernel/dma/mapping.c | 20 ++++++++++++++++++++ > 2 files changed, 25 insertions(+) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 8074a3b5c807..6906edde505d 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -410,6 +410,7 @@ static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) > { > return dma_dev_need_sync(dev) ? __dma_need_sync(dev, dma_addr) : false; > } > +bool dma_need_unmap(struct device *dev); > #else /* !CONFIG_HAS_DMA || !CONFIG_DMA_NEED_SYNC */ > static inline bool dma_dev_need_sync(const struct device *dev) > { > @@ -435,6 +436,10 @@ static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) > { > return false; > } > +static inline bool dma_need_unmap(struct device *dev) > +{ > + return false; > +} > #endif /* !CONFIG_HAS_DMA || !CONFIG_DMA_NEED_SYNC */ > > struct page *dma_alloc_pages(struct device *dev, size_t size, > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c > index 864a1121bf08..daa97a650778 100644 > --- a/kernel/dma/mapping.c > +++ b/kernel/dma/mapping.c > @@ -442,6 +442,26 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr) > } > EXPORT_SYMBOL_GPL(__dma_need_sync); > > +/** > + * dma_need_unmap - does this device need dma_unmap_* operations > + * @dev: device to check > + * > + * If this function returns %false, drivers can skip calling dma_unmap_* after > + * finishing an I/O. This function must be called after all mappings that might > + * need to be unmapped have been performed. In terms of the unmap call itself, why don't we just use dma_skip_sync to short-cut dma_direct_unmap_*() and make sure it's as cheap as possible? In terms of not having to unmap implying not having to store addresses at all, it doesn't seem super-useful when you still have to store them for long enough to find out that you don't :/ Thanks, Robin. > + */ > +bool dma_need_unmap(struct device *dev) > +{ > + if (!dma_map_direct(dev, get_dma_ops(dev))) > + return true; > +#ifdef CONFIG_DMA_NEED_SYNC > + if (!dev->dma_skip_sync) > + return true; > +#endif > + return IS_ENABLED(CONFIG_DMA_API_DEBUG); > +} > +EXPORT_SYMBOL_GPL(dma_need_unmap); > + > static void dma_setup_need_sync(struct device *dev) > { > const struct dma_map_ops *ops = get_dma_ops(dev);