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commit 9e0e59993df0601cddb95c4f6c61aa3d5e753c00 upstream. On a Thinkpad s30 (Pentium III / i440MX, Lynx3DM), running fbtest or X will crash the machine instantly, because the VRAM/framebuffer is not mapped correctly. On SM712, the framebuffer starts at the beginning of address space, but SM720's framebuffer starts at the 1 MiB offset from the beginning. However, sm712fb fails to take this into account, as a result, writing to the framebuffer will destroy all the registers and kill the system immediately. Another problem is the driver assumes 8 MiB of VRAM for SM720, but some SM720 system, such as this IBM Thinkpad, only has 4 MiB of VRAM. Fix this problem by removing the hardcoded VRAM size, adding a function to query the amount of VRAM from register MCR76 on SM720, and adding proper framebuffer offset. Please note that the memory map may have additional problems on Big-Endian system, which is not available for testing by myself. But I highly suspect that the original code is also broken on Big-Endian machines for SM720, so at least we are not making the problem worse. More, the driver also assumed SM710/SM712 has 4 MiB of VRAM, but it has a 2 MiB version as well, and used in earlier laptops, such as IBM Thinkpad 240X, the driver would probably crash on them. I've never seen one of those machines and cannot fix it, but I have documented these problems in the comments. Signed-off-by: Yifeng Li <tomli@tomli.me> Tested-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com> Cc: Teddy Wang <teddy.wang@siliconmotion.com> Cc: <stable@vger.kernel.org> # v4.4+ Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.