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SubjectRe: [PATCH] i2c: i2c-tiny-usb: fix buffer not being DMA capable
Hi Greg,

On Thu, May 04, 2017 at 08:27:09AM -0700, Greg KH wrote:
> On Thu, May 04, 2017 at 02:56:32PM +0200, Sebastian Reichel wrote:
> > The i2c-tiny-usb driver generates the following trace and fails to
> > read or write data on a v4.9 or newer kernels. This patch avoids the
> > problem by allocating a DMA capable buffer for data transfer.
> >
> > [ 17.504959] ------------[ cut here ]------------
> > [ 17.505488] WARNING: CPU: 0 PID: 93 at drivers/usb/core/hcd.c:1587 usb_hcd_map_urb_for_dma+0x37c/0x570
> > [ 17.506545] transfer buffer not dma capable
> > [ 17.507022] Modules linked in:
> > [ 17.507370] CPU: 0 PID: 93 Comm: i2cdetect Not tainted 4.11.0-rc8+ #10
> > [ 17.508103] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> > [ 17.509039] Call Trace:
> > [ 17.509320] ? dump_stack+0x5c/0x78
> > [ 17.509714] ? __warn+0xbe/0xe0
> > [ 17.510073] ? warn_slowpath_fmt+0x5a/0x80
> > [ 17.510532] ? nommu_map_sg+0xb0/0xb0
> > [ 17.510949] ? usb_hcd_map_urb_for_dma+0x37c/0x570
> > [ 17.511482] ? usb_hcd_submit_urb+0x336/0xab0
> > [ 17.511976] ? wait_for_completion_timeout+0x12f/0x1a0
> > [ 17.512549] ? wait_for_completion_timeout+0x65/0x1a0
> > [ 17.513125] ? usb_start_wait_urb+0x65/0x160
> > [ 17.513604] ? usb_control_msg+0xdc/0x130
> > [ 17.514061] ? usb_xfer+0xa4/0x2a0
> > [ 17.514445] ? __i2c_transfer+0x108/0x3c0
> > [ 17.514899] ? i2c_transfer+0x57/0xb0
> > [ 17.515310] ? i2c_smbus_xfer_emulated+0x12f/0x590
> > [ 17.515851] ? _raw_spin_unlock_irqrestore+0x11/0x20
> > [ 17.516408] ? i2c_smbus_xfer+0x125/0x330
> > [ 17.516876] ? i2c_smbus_xfer+0x125/0x330
> > [ 17.517329] ? i2cdev_ioctl_smbus+0x1c1/0x2b0
> > [ 17.517824] ? i2cdev_ioctl+0x75/0x1c0
> > [ 17.518248] ? do_vfs_ioctl+0x9f/0x600
> > [ 17.518671] ? vfs_write+0x144/0x190
> > [ 17.519078] ? SyS_ioctl+0x74/0x80
> > [ 17.519463] ? entry_SYSCALL_64_fastpath+0x1e/0xad
> > [ 17.519959] ---[ end trace d047c04982f5ac50 ]---
> >
> > Cc: <stable@vger.kernel.org> # Kernel 4.9+
>
> This has been a USB core requirement since the 2.2 days, it's only since
> 4.9 that most people have started to notice this. So backporting it to
> anything that it can go to is best to have happen :)

I intentionally did not add a "Fixes:" for the commit in 4.9, since
I assumed that to be the case (did not bisect to the commit either).
OTOH the driver worked before v4.9, so I thought I would reduce your
(and the other backporters) workload - users won't care.

Looks like it added more work now, so I will drop the comment in
PATCHv2 and leave it to stable porters figuring out if they want
to backport it.

> > + void *dmadata = kmalloc(len, GFP_KERNEL);
> > + void *dmadata = kmemdup(data, len, GFP_KERNEL);
>
> No error checking?

Coming in PATCHv2.

-- Sebastian
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