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
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