On Thu, Sep 12, 2013 at 08:55:54AM -0600, Stephen Warren wrote: > On 09/12/2013 07:03 AM, Pawel Moll wrote: > > Ok, so I'll make it a arm,pl11x,specific property. Actually two > > properties - one bit I missed was the dual STN panel case, where they > > have separate frame buffers. Something along the lines of: > > > > Optional: > > > > - arm,pl11x,framebuffer-base: a pair of two values, address and size, > > defining the framebuffer for the upper > > (or the only one) panel > > - arm,pl11x,lower-framebuffer-base: as above, for the lower STN panel, > > when present > > > > Being very hardware-specific, it covers all possible quirky scenarios, > > at the same time does not exclude the option of using the CMA region > > phandles, if a particular system needed it. > > What do "upper" and "lower" mean in this context? I assume this somehow > refers to placement of the displays on the board. CLCD is only one controller - it can only produce one image from one framebuffer. What this refers to is a requirement for dual STN displays - rather than starting at one corner and working logically to the opposite corner, these start at one corner and half way through the display at the same time. So you scan out the upper half of the image at the same time that you scan out the lower half of the image. In order to give an image on the display where the conventional formula works: address = start + y * bytes_per_line + x * bits_per_pixel / 8 this means that the "upper" and "lower" start addresses are related to the parameters of the display - you want the lower half to start at the address where y = panel_y_res / 2 and x = 0. You may also wish to change the start address (if you have enough RAM) to support page flipping - where you switch between two framebuffers - one which is currently being displayed while the other is being updated by the CPU. You would use this to provide smooth video playback for example. So, DT has no business directly encoding this information - it should be calculated from the information provided by the panel and the timings required, and all that the CLCD driver should know is that "we have this RAM which starts here, and extends for N bytes" - or to use system memory instead. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
