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We shouldn't attempt to DMA map the message buffers passed into this driver from the i2c core unless the message we're mapping have been properly setup for DMA. The i2c core indicates such a situation by setting the I2C_M_DMA_SAFE flag, so check for that flag before using DMA mode. We can also bounce the buffer if it isn't already mapped properly by using the i2c_get_dma_safe_msg_buf() APIs, so do that when we want to use DMA for a message. This fixes a problem where the kernel oopses cleaning pages for a buffer that's mapped into the vmalloc space. The pages are returned from request_firmware() and passed down directly to the i2c master to write to the i2c touchscreen device. Mapping vmalloc buffers with dma_map_single() won't work reliably, causing an oops like below: Unable to handle kernel paging request at virtual address ffffffc01391d000 ... Reported-by: Philip Chen <philipchen@chromium.org> Signed-off-by: Stephen Boyd <swboyd@chromium.org> Reviewed-by: Douglas Anderson <dianders@chromium.org> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.