Am 28.12.2017 um 16:29 schrieb Michal Suchánek:
On Mon, 25 Dec 2017 22:18:45 +0100 Alexander Graf <agraf@suse.de> wrote:
On 25.12.17 18:36, Michal Suchánek wrote:
Hello,
for testing I installed stable and master kernel on Leap 42.3 E20 image.
Initially it would work fine but later I would have to add cma=256MB (some random value found on a forum) to kernel commandline for video output to work.
Has the cma requirement changed as a result of recent vc4 changes?
No, it's always been there. In the early days we had a default CMA size of 64MB IIRC, but given that a good number of platforms don't need any CMA space at all, it seemed like a wasted allocation.
For the RPi, we added a CMA command line parameter to the kiwi file to override the default 0MB allocation. Maybe something went wrong and that change never happened in Leap 42.3?
Maybe 42.3 dose not really need it because it does not have the driver in the kernel or still has the 64MB default.
Can the kernel allocate the required size automatically?
Yes, if you tell it on the kernel command line :).
I do not have to tell the kernel I have an integrated Intel graphics card and it can still allocate its buffers just fine.
Really, CMA is all about reserving a range of memory space for contiguous allocations, so all allocations happening inside that range have to be movable and can be forced to move at any given point in time.
I'm not quite sure what the kernel should do more automatically than it already does.
Just allocate the buffer whenever there is a vc4 card :)
The RPi does not have an IOMMU, so it needs to pre-allocate a contiguous hunk of memory, unlike other Intel or Arm based systems. HTE, Andreas -- SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- To unsubscribe, e-mail: opensuse-arm+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-arm+owner@opensuse.org