On Sun, Mar 17, 2019 at 06:25:01AM +0800, Yifeng Li wrote: > 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@xxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # v4.4+ Tested-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx> -- Regards Sudip
