Re: simple-framebuffer enquire

From: Hans de Goede
Date: Tue Jun 26 2018 - 09:36:37 EST


Hi,

On 26-06-18 15:29, Michael Nazzareno Trimarchi wrote:
Hi

to be more specific

On Tue, Jun 26, 2018 at 3:06 PM, Michael Nazzareno Trimarchi
<michael@xxxxxxxxxxxxxxxxxxxx> wrote:
Hi

On Tue., 26 Jun. 2018, 12:01 pm Hans de Goede, <hdegoede@xxxxxxxxxx> wrote:

Hi,

On 25-06-18 15:29, Michael Nazzareno Trimarchi wrote:
Hi Hans

In order to let it even registered the simplefb I have added this
change. According on what I understand
from the code seems that this is the way to acquire memory with the
correct attribute

diff --git a/drivers/video/fbdev/simplefb.c
b/drivers/video/fbdev/simplefb.c
index a3c44ec..7e61ce3 100644
--- a/drivers/video/fbdev/simplefb.c
+++ b/drivers/video/fbdev/simplefb.c
@@ -466,8 +466,8 @@ static int simplefb_probe(struct platform_device
*pdev)

info->fbops = &simplefb_ops;
info->flags = FBINFO_DEFAULT | FBINFO_MISC_FIRMWARE;
- info->screen_base = ioremap_wc(info->fix.smem_start,
- info->fix.smem_len);
+ info->screen_base = arch_memremap_wb(info->fix.smem_start,
+ info->fix.smem_len);

I'm not sure why you need this? wb certainly is not optimal
for a framebuffer, the existing wc mapping is really what you
want.


Well in this way raise a WARN and get a nice NULL on memory remap on imx6ull
SoC


[ 0.397484] WARNING: CPU: 0 PID: 1 at arch/arm/mm/ioremap.c:303
__arm_ioremap_pfn_caller+0x80/0x1cc


This is causes by a mismatch in memory attributes, which means the
memory is already mapped by the kernel as regular RAM and may
already be used for other purposes by the kernel!

Memory used by a simplefb framebuffer must be reserved by the
bootloader, so that it does not get used by the kernel as regular
RAM. See e.g.:

http://git.denx.de/?p=u-boot.git;a=blob;f=drivers/video/sunxi/sunxi_display.c

Near the end of the file where the framebuffer RAM gets excluded from
the memory-range reported to the kernel as usable RAM. Note this relies
on the u-boot sunxi video code putting the framebuffer at the end of the
RAM.

Regards,

Hans