Hi,
On 12-08-15 12:45, Ian Campbell wrote:
On Wed, 2015-08-05 at 17:17 +0200, Hans de Goede wrote:
sunxi_display.fb_size =
(mode->xres * mode->yres * 4 + 0xfff) & ~0xfff;
+> > overscan_offset = (overscan_y * mode->xres + overscan_x) * 4; +> > /* We want to keep the fb_base for simplefb page aligned, where as +> > * the sunxi dma engines will happily accept an unaligned address. */ +> > if (overscan_offset) +> > > sunxi_display.fb_size += 0x1000;
Why plus 4K regardless of the magnitude of overscan_offset? What if it was 0x1004?
If overscan offset is 0x1004 then we make the simplefb start point to fb_base + 0x2000:
sunxi_display.fb_addr = gd->fb_base sunxi_display.fb_addr += (overscan_offset + 0xfff) & ~0xfff
And make the dma engine start at fb_base + 0xffc:
fb_dma_addr = gd->fb_base fb_dma_addr += 0x1000 - (overscan_offset & 0xfff)
Notice how we make the dma_engine start at less then 0x1000 offset of fb_base, so making fb_size 0x1000 larger is enough.
Basically to page-align the start of the simplefb / sunxi_display.fb_addr we only need a single page, the rest we can get by offsetting sunxi_display.fb_addr from fb_base by a multiple of the page size.
Also, what's the link between fb_base's alignment and fb_size which is implied by the comment?
To align we need a page extra size as the dma-engine may start at an offset of up-to a page-size from gd->fb_base and the dma-engine will dma a full framebuffer size, including the black borders.
gd->fb_base = gd->bd->bi_dram[0].start +
gd->bd->bi_dram[0].size - sunxi_display.fb_size;sunxi_engines_init();
-> > sunxi_mode_set(mode, gd->fb_base - CONFIG_SYS_SDRAM_BASE);
+> > fb_dma_addr = gd->fb_base - CONFIG_SYS_SDRAM_BASE; +> > sunxi_display.fb_addr = gd->fb_base; +> > if (overscan_offset) { +> > > fb_dma_addr += 0x1000 - (overscan_offset & 0xfff); +> > > sunxi_display.fb_addr += (overscan_offset + 0xfff) & ~0xfff; +> > > memset((void *)gd->fb_base, 0, sunxi_display.fb_size); +> > > flush_cache(gd->fb_base, sunxi_display.fb_size); +> > }
Hrm, I think this starts to answer, but I'm still not sure I follow, sorry.
Correct this is the answer, sorry for the tricky maths, this is the best solution without wasting a ton of memory with large overscans.
I hope the above explanation helps, if not keep asking.
sunxi_mode_set(mode, fb_dma_addr);
/*
- These are the only members of this structure that are used. All the
- others are driver specific. There is nothing to decribe pitch or
Pre-existing typo "describe".
Will fix,
Regards,
Hans