Allocation of frame buffer at a specific memory range or address
On Sat, Apr 16, 2016 at 2:07 AM, Vineet Gupta
wrote:
> On Friday 15 April 2016 09:18 PM, Alexey Brodkin wrote:
>
>> And now the question is how to force DRM subsystem or just that driver
>> to use whatever predefined (say via device tree) location in memory
>> for data buffer allocation.
>
> It seems this is pretty easy to do with DT reserved-memory binding.
>
> You need to partition memory into @memory and @reserved-memory.
> Later can be subdivided into more granular regions and your driver can refer
> to
> one of the regions.
jfyi, it might be useful to look at msm_init_vram() which has support
to wrap vram carveout as gem buffer, for exact same purpose..
BR,
-R
> Something like below (untested)
>
> + memory {
> + device_type = "memory";
> + reg = <0x0 0x8000 0x0 0xA000>;
> + #address-cells = <2>;
> + #size-cells = <2>;
> + };
> +
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <2>;
> + ranges;
> + /* This memory bypasses IOC port */
> + fb_reserved at A000 {
> + reg = <0x0 0xA000 0x0 0xAF00>;
> + #address-cells = <2>;
> + #size-cells = <2>;
> + /* no-map; */
> + };
> + };
> +
> +
> + fb0: video at 1230 {
> + memory-region = <_reserved>;
> + /* ... */
> + };
>
> This might also need a DT helper in ARC mm init code.
>
> + early_init_fdt_scan_reserved_mem();
>
> HTH,
> -Vineet
Allocation of frame buffer at a specific memory range or address
On Friday 15 April 2016 09:18 PM, Alexey Brodkin wrote:
> And now the question is how to force DRM subsystem or just that driver
> to use whatever predefined (say via device tree) location in memory
> for data buffer allocation.
It seems this is pretty easy to do with DT reserved-memory binding.
You need to partition memory into @memory and @reserved-memory.
Later can be subdivided into more granular regions and your driver can refer to
one of the regions.
Something like below (untested)
+ memory {
+ device_type = "memory";
+ reg = <0x0 0x8000 0x0 0xA000>;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ };
+
+ reserved-memory {
+ #address-cells = <2>;
+ #size-cells = <2>;
+ ranges;
+ /* This memory bypasses IOC port */
+ fb_reserved at A000 {
+ reg = <0x0 0xA000 0x0 0xAF00>;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ /* no-map; */
+ };
+ };
+
+
+ fb0: video at 1230 {
+ memory-region = <_reserved>;
+ /* ... */
+ };
This might also need a DT helper in ARC mm init code.
+ early_init_fdt_scan_reserved_mem();
HTH,
-Vineet
Allocation of frame buffer at a specific memory range or address
On Fri, Apr 15, 2016 at 5:48 PM, Alexey Brodkin wrote: > Hello, > > I'm wondering if there's a way to force kernel to allocate backing > memory for frame buffer in a special location? > > A little bit of background below. > I continue to work on DRM driver for ARC PGU, latest > is v5 and available here - https://lkml.org/lkml/2016/3/28/170 > > In current state everything more or less works but I'd like to > implement one improvement - I'd like to have an ability to specify > where in memory will be allocated frame-buffer's backing storage area. > I.e. buffer which will be read by PGU hardware. > > Currently we use whatever DRM susbsystem put in "gem->paddr". > That's a snippet of the code which tells PGU hardware > which memory location to scan for data: > ->8 > arcpgu = crtc_to_arcpgu_priv(plane->state->crtc); > gem = drm_fb_cma_get_gem_obj(plane->state->fb, 0); > > /* Telling PGU hardware where is data to read */ > arc_pgu_write(arcpgu, ARCPGU_REG_BUF0_ADDR, gem->paddr); > ->8 > > But we may use a special memory area which works better > for that case, i.e. for example could be accessed faster by both > CPU and PGU hardware (like on-chip SRAM as opposed to external DDR). > > And now the question is how to force DRM subsystem or just that driver > to use whatever predefined (say via device tree) location in memory > for data buffer allocation. > > All thoughts on this are more than welcome. Instead of using cma, you need to create your own gem buffer objects and allocate the memory for those from wherever you want to. Or you can do a mix of cma gem allocations and other objects (e.g. omapdrm does that). Using cma (which simply uses dma_alloc_coherent underneath) is just a convenient way, and generally the right choice on SoC display drivers. There's no need to use that at all, KMS is fully agnostic to how/what your underlying buffer objects even are. You could have allocations in some sepcial secure memory that only the gpu could even read/write, as another example. Maybe we need to make this part in the overview docs better? -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
