media: ivtv: add parameter to enable ivtvfb on x86 PAT systems
ivtvfb was previously disabled for x86 PAT-enabled systems by commit 1bf1735b ("x86/mm/pat, drivers/media/ivtv: Use arch_phys_wc_add() and require PAT disabled") as a workaround to abstract MTRR code away from device drivers. The driver is not easily upgradable to the PAT-aware ioremap_wc() API since the firmware hides the address ranges that should be marked write-combined from the driver. However, since a write-combined cache on the framebuffer is only a performance enhancement not a requirement for the framebuffer to function, completely disabling the driver in this configuration is not necessary. Add force_pat module parameter and a corresponding kernel configuration parameter to optionally force initialization on PAT-enabled x86 systems with a warning about the lack of write-combined caching, and document the reasons the driver cannot be easily updated to support wc caching on all systems. Signed-off-by: Nick French <naf@ou.edu> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> [hverkuil-cisco@xs4all.nl: fix typo, split long pr_ lines up] Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
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