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Date: Fri, 17 Dec 2010 14:42:21 -0800
From: rmorell@...dia.com
To: Greg KH <gregkh@...e.de>
Cc: David Brownell <dbrownell@...rs.sourceforge.net>,
Benoit Goby <benoit@...roid.com>,
Alan Stern <stern@...land.harvard.edu>,
Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
Matthew Wilcox <willy@...ux.intel.com>,
Ming Lei <tom.leiming@...il.com>,
Jacob Pan <jacob.jun.pan@...el.com>,
Olof Johansson <olof@...om.net>,
Erik Gilling <konkers@...roid.com>,
Colin Cross <ccross@...roid.com>,
"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] USB: ehci: tegra: Align DMA transfers to 32 bytes
On Fri, Dec 17, 2010 at 02:35:02PM -0800, Greg KH wrote:
> On Fri, Dec 17, 2010 at 01:58:49PM -0800, Robert Morell wrote:
> > The Tegra2 USB controller doesn't properly deal with misaligned DMA
> > buffers, causing corruption. This is especially prevalent with USB
> > network adapters, where skbuff alignment is often in the middle of a
> > 4-byte dword.
> >
> > To avoid this, allocate a temporary buffer for the DMA if the provided
> > buffer isn't sufficiently aligned.
> >
> > Signed-off-by: Robert Morell <rmorell@...dia.com>
> > Reviewed-by: Scott Williams <scwilliams@...dia.com>
> > Reviewed-by: Janne Hellsten <jhellsten@...dia.com>
> > ---
> > drivers/usb/host/ehci-tegra.c | 94 +++++++++++++++++++++++++++++++++++++++++
> > include/linux/usb.h | 1 +
> > 2 files changed, 95 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
> > index d990c1c..a75e4db 100644
> > --- a/drivers/usb/host/ehci-tegra.c
> > +++ b/drivers/usb/host/ehci-tegra.c
> > @@ -32,6 +32,10 @@
> > #define TEGRA_USB_USBMODE_HOST (3 << 0)
> > #define TEGRA_USB_PORTSC1_PTC(x) (((x) & 0xf) << 16)
> >
> > +#define TEGRA_USB_DMA_ALIGN 32
> > +
> > +#define URB_ALIGNED_TEMP_BUFFER 0x80000000
> > +
> > struct tegra_ehci_context {
> > bool valid;
> > u32 command;
> > @@ -457,6 +461,94 @@ static int tegra_ehci_bus_resume(struct usb_hcd *hcd)
> > }
> > #endif
> >
> > +struct temp_buffer {
> > + void *kmalloc_ptr;
> > + void *old_xfer_buffer;
> > + u8 data[0];
> > +};
> > +
> > +static void free_temp_buffer(struct urb *urb)
> > +{
> > + enum dma_data_direction dir;
> > + struct temp_buffer *temp;
> > +
> > + if (!(urb->transfer_flags & URB_ALIGNED_TEMP_BUFFER))
> > + return;
> > +
> > + dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> > +
> > + temp = container_of(urb->transfer_buffer, struct temp_buffer,
> > + data);
> > +
> > + if (dir == DMA_FROM_DEVICE)
> > + memcpy(temp->old_xfer_buffer, temp->data,
> > + urb->transfer_buffer_length);
> > + urb->transfer_buffer = temp->old_xfer_buffer;
> > + kfree(temp->kmalloc_ptr);
> > +
> > + urb->transfer_flags &= ~URB_ALIGNED_TEMP_BUFFER;
> > +}
> > +
> > +static int alloc_temp_buffer(struct urb *urb, gfp_t mem_flags)
> > +{
> > + enum dma_data_direction dir;
> > + struct temp_buffer *temp, *kmalloc_ptr;
> > + size_t kmalloc_size;
> > + void *data;
> > +
> > + if (urb->num_sgs || urb->sg ||
> > + urb->transfer_buffer_length == 0 ||
> > + !((uintptr_t)urb->transfer_buffer & (TEGRA_USB_DMA_ALIGN - 1)))
> > + return 0;
> > +
> > + dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> > +
> > + /* Allocate a buffer with enough padding for alignment */
> > + kmalloc_size = urb->transfer_buffer_length +
> > + sizeof(struct temp_buffer) + TEGRA_USB_DMA_ALIGN - 1;
> > +
> > + kmalloc_ptr = kmalloc(kmalloc_size, mem_flags);
> > + if (!kmalloc_ptr)
> > + return -ENOMEM;
> > +
> > + /* Position our struct temp_buffer such that data is aligned */
> > + temp = PTR_ALIGN(kmalloc_ptr + 1, TEGRA_USB_DMA_ALIGN) - 1;
> > +
> > + temp->kmalloc_ptr = kmalloc_ptr;
> > + temp->old_xfer_buffer = urb->transfer_buffer;
> > + if (dir == DMA_TO_DEVICE)
> > + memcpy(temp->data, urb->transfer_buffer,
> > + urb->transfer_buffer_length);
> > + urb->transfer_buffer = temp->data;
> > +
> > + BUILD_BUG_ON(!(URB_ALIGNED_TEMP_BUFFER & URB_DRIVER_PRIVATE));
>
> See below why this should be removed
>
> > + urb->transfer_flags |= URB_ALIGNED_TEMP_BUFFER;
> > +
> > + return 0;
> > +}
> > +
> > +static int tegra_ehci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > + gfp_t mem_flags)
> > +{
> > + int ret;
> > +
> > + ret = alloc_temp_buffer(urb, mem_flags);
> > + if (ret)
> > + return ret;
> > +
> > + ret = usb_hcd_map_urb_for_dma(hcd, urb, mem_flags);
> > + if (ret)
> > + free_temp_buffer(urb);
> > +
> > + return ret;
> > +}
> > +
> > +static void tegra_ehci_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
> > +{
> > + usb_hcd_unmap_urb_for_dma(hcd, urb);
> > + free_temp_buffer(urb);
> > +}
> > +
> > static const struct hc_driver tegra_ehci_hc_driver = {
> > .description = hcd_name,
> > .product_desc = "Tegra EHCI Host Controller",
> > @@ -472,6 +564,8 @@ static const struct hc_driver tegra_ehci_hc_driver = {
> > .shutdown = tegra_ehci_shutdown,
> > .urb_enqueue = ehci_urb_enqueue,
> > .urb_dequeue = ehci_urb_dequeue,
> > + .map_urb_for_dma = tegra_ehci_map_urb_for_dma,
> > + .unmap_urb_for_dma = tegra_ehci_unmap_urb_for_dma,
> > .endpoint_disable = ehci_endpoint_disable,
> > .endpoint_reset = ehci_endpoint_reset,
> > .get_frame_number = ehci_get_frame,
> > diff --git a/include/linux/usb.h b/include/linux/usb.h
> > index 35fe6ab..cd07173 100644
> > --- a/include/linux/usb.h
> > +++ b/include/linux/usb.h
> > @@ -975,6 +975,7 @@ extern int usb_disabled(void);
> > #define URB_SETUP_MAP_SINGLE 0x00100000 /* Setup packet DMA mapped */
> > #define URB_SETUP_MAP_LOCAL 0x00200000 /* HCD-local setup packet */
> > #define URB_DMA_SG_COMBINED 0x00400000 /* S-G entries were combined */
> > +#define URB_DRIVER_PRIVATE 0x80000000 /* For driver-private use */
>
> Um, what? You are using this for a build check, which seems pointless
> as you already modified the code to not need this.
>
> So it doesn't look like this is needed, right?
The intention was to reserve space in the URB flags for
implementation-specific use. This placeholder should keep anybody from
adding driver-agnostic flags to that mask. The BUILD_BUG_ON is intended
to make sure that the driver private space doesn't move out from under
the Tegra-specific flag.
Thanks,
Robert
> thanks,
>
> greg k-h
>
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