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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Ohad Ben-Cohen <ohad@wizery.com>,
	devicetree@vger.kernel.org,
	Florian Fainelli <f.fainelli@gmail.com>,
	linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org,
	linux-pci@vger.kernel.org, Frank Rowand <frowand.list@gmail.com>,
	linux-usb@vger.kernel.org, linux-remoteproc@vger.kernel.org,
	Russell King <linux@armlinux.org.uk>,
	linux-acpi@vger.kernel.org, iommu@lists.linux-foundation.org,
	Rob Herring <robh+dt@kernel.org>,
	Jim Quinlan <james.quinlan@broadcom.com>,
	Santosh Shilimkar <ssantosh@kernel.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Robin Murphy <robin.murphy@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 5/6] usb: don't inherity DMA properties for USB devices
Date: Mon, 14 Sep 2020 09:51:40 +0200	[thread overview]
Message-ID: <20200914075140.GA1033580@kroah.com> (raw)
In-Reply-To: <20200914073343.1579578-6-hch@lst.de>

On Mon, Sep 14, 2020 at 09:33:42AM +0200, Christoph Hellwig wrote:
> As the comment in usb_alloc_dev correctly states, drivers can't use
> the DMA API on usb device, and at least calling dma_set_mask on them
> is highly dangerous.  Unlike what the comment states upper level drivers
> also can't really use the presence of a dma mask to check for DMA
> support, as the dma_mask is set by default for most busses.
> 
> Setting the dma_mask comes from "[PATCH] usbcore dma updates (and doc)"
> in BitKeeper times, as it seems like it was primarily for setting the
> NETIF_F_HIGHDMA flag in USB drivers, something that has long been
> fixed up since.
> 
> Setting the dma_pfn_offset comes from commit b44bbc46a8bb
> ("usb: core: setup dma_pfn_offset for USB devices and, interfaces"),
> which worked around the fact that the scsi_calculate_bounce_limits
> functions wasn't going through the proper driver interface to query
> DMA information, but that function was removed in commit 21e07dba9fb1
> ("scsi: reduce use of block bounce buffers") years ago.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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  reply	other threads:[~2020-09-14  7:51 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-14  7:33 support range based offsets in dma-direct v2 Christoph Hellwig
2020-09-14  7:33 ` [PATCH 1/6] ARM/dma-mapping: remove a __arch_page_to_dma #error Christoph Hellwig
2020-09-14  7:33 ` [PATCH 2/6] ARM/dma-mapping: remove dma_to_virt Christoph Hellwig
2020-09-14  7:33 ` [PATCH 3/6] ARM/dma-mapping: move various helpers from dma-mapping.h to dma-direct.h Christoph Hellwig
2020-09-14  7:33 ` [PATCH 4/6] ARM/keystone: move the DMA offset handling under ifdef CONFIG_ARM_LPAE Christoph Hellwig
2020-09-14  7:33 ` [PATCH 5/6] usb: don't inherity DMA properties for USB devices Christoph Hellwig
2020-09-14  7:51   ` Greg Kroah-Hartman [this message]
2020-09-14  7:33 ` [PATCH 6/6] dma-mapping: introduce DMA range map, supplanting dma_pfn_offset Christoph Hellwig
2020-09-14 23:01   ` Mathieu Poirier
2020-09-15  5:41     ` Christoph Hellwig
2020-09-15 19:55       ` Mathieu Poirier
2020-09-16  6:13         ` Christoph Hellwig
2020-09-16  6:14 support range based offsets in dma-direct v3 Christoph Hellwig
2020-09-16  6:14 ` [PATCH 5/6] usb: don't inherity DMA properties for USB devices Christoph Hellwig

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