Am 28.12.2017 um 16:29 schrieb Michal Suchánek: > On Mon, 25 Dec 2017 22:18:45 +0100 > Alexander Graf <[email protected]> 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: [email protected] To contact the owner, e-mail: [email protected]
