From: Greg KH <greg@kroah.com>
To: Christoph Hellwig <hch@lst.de>
Cc: devicetree@vger.kernel.org,
Florian Fainelli <f.fainelli@gmail.com>,
linux-sh@vger.kernel.org, Frank Rowand <frowand.list@gmail.com>,
linux-usb@vger.kernel.org, linux-pci@vger.kernel.org,
Russell King <linux@armlinux.org.uk>,
linux-kernel@vger.kernel.org, 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 3/3] dma-mapping: introduce DMA range map, supplanting dma_pfn_offset
Date: Thu, 10 Sep 2020 18:12:24 +0200 [thread overview]
Message-ID: <20200910161224.GB1158578@kroah.com> (raw)
In-Reply-To: <20200910091351.GA25883@lst.de>
On Thu, Sep 10, 2020 at 11:13:51AM +0200, Christoph Hellwig wrote:
> On Thu, Sep 10, 2020 at 09:53:51AM +0200, Greg KH wrote:
> > > /*
> > > * Please refer to usb_alloc_dev() to see why we set
> > > - * dma_mask and dma_pfn_offset.
> > > + * dma_mask and dma_range_map.
> > > */
> > > intf->dev.dma_mask = dev->dev.dma_mask;
> > > - intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset;
> > > + if (dma_direct_copy_range_map(&intf->dev, &dev->dev))
> > > + dev_err(&dev->dev, "failed to copy DMA map\n");
> >
> > We tell the user, but then just keep on running? Is there anything that
> > we can do here?
> >
> > If not, why not have dma_direct_copy_range_map() print out the error?
>
> At least for USB I'm pretty sure this isn't required at all. I've been
> running with the patch below on my desktop for two days now trying all
> the usb toys I have (in addition to grepping for obvious abuses in
> the drivers). remoteproc is a different story, but the DMA handling
> seems there is sketchy to start with..
>
> ---
> >From 8bae3e6833f2ca431dcfcbc8f9cced7d5e972a01 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Wed, 9 Sep 2020 08:28:59 +0200
> Subject: usb: don't inherity DMA properties for USB devices
>
> 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.
>
> Remove the copying over of DMA information, and remove the now unused
> dma_direct_copy_range_map export.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/usb/core/message.c | 7 -------
> drivers/usb/core/usb.c | 13 -------------
> kernel/dma/direct.c | 1 -
> 3 files changed, 21 deletions(-)
>
> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index 935ee98e049f65..9e45732dc1d1d1 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -1954,13 +1954,6 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
> intf->dev.bus = &usb_bus_type;
> intf->dev.type = &usb_if_device_type;
> intf->dev.groups = usb_interface_groups;
> - /*
> - * Please refer to usb_alloc_dev() to see why we set
> - * dma_mask and dma_range_map.
> - */
> - intf->dev.dma_mask = dev->dev.dma_mask;
> - if (dma_direct_copy_range_map(&intf->dev, &dev->dev))
> - dev_err(&dev->dev, "failed to copy DMA map\n");
> INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
> intf->minor = -1;
> device_initialize(&intf->dev);
> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> index 23d451f6894d70..9b4ac4415f1a47 100644
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -599,19 +599,6 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
> dev->dev.bus = &usb_bus_type;
> dev->dev.type = &usb_device_type;
> dev->dev.groups = usb_device_groups;
> - /*
> - * Fake a dma_mask/offset for the USB device:
> - * We cannot really use the dma-mapping API (dma_alloc_* and
> - * dma_map_*) for USB devices but instead need to use
> - * usb_alloc_coherent and pass data in 'urb's, but some subsystems
> - * manually look into the mask/offset pair to determine whether
> - * they need bounce buffers.
> - * Note: calling dma_set_mask() on a USB device would set the
> - * mask for the entire HCD, so don't do that.
> - */
> - dev->dev.dma_mask = bus->sysdev->dma_mask;
> - if (dma_direct_copy_range_map(&dev->dev, bus->sysdev))
> - dev_err(&dev->dev, "failed to copy DMA map\n");
> set_dev_node(&dev->dev, dev_to_node(bus->sysdev));
> dev->state = USB_STATE_ATTACHED;
> dev->lpm_disable_count = 1;
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index fc815f7375e282..3af257571a3b42 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -552,4 +552,3 @@ int dma_direct_copy_range_map(struct device *to, struct device *from)
> to->dma_range_map = new_map;
> return 0;
> }
> -EXPORT_SYMBOL_GPL(dma_direct_copy_range_map);
If you think this is safe to do, great, but for some reason I thought
host controllers wanted this information, and that the scsi layer was
the offending layer that also wanted this type of thing. But it's been
a really long time so I don't remember for sure, sorry.
thanks,
greg k-h
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next prev parent reply other threads:[~2020-09-10 16:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 5:40 support range based offsets in dma-direct Christoph Hellwig
2020-09-10 5:40 ` [PATCH 1/3] ARM/dma-mapping: move various helpers from dma-mapping.h to dma-direct.h Christoph Hellwig
2020-09-10 18:02 ` Robin Murphy
2020-09-11 6:25 ` Christoph Hellwig
2020-09-10 5:40 ` [PATCH 2/3] ARM/keystone: move the DMA offset handling under ifdef CONFIG_ARM_LPAE Christoph Hellwig
2020-09-11 11:12 ` Robin Murphy
2020-09-11 11:15 ` Russell King - ARM Linux admin
2020-09-11 11:27 ` Robin Murphy
2020-09-11 18:00 ` santosh.shilimkar
2020-09-10 5:40 ` [PATCH 3/3] dma-mapping: introduce DMA range map, supplanting dma_pfn_offset Christoph Hellwig
2020-09-10 7:53 ` Greg KH
2020-09-10 9:13 ` Christoph Hellwig
2020-09-10 16:12 ` Greg KH [this message]
2020-09-11 16:12 ` Robin Murphy
2020-09-12 6:46 ` Christoph Hellwig
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