[Nouveau] [PATCH v3 4/6] instmem/gk20a: use DMA attributes

[Alexandre Courbot]

On Wed, Feb 18, 2015 at 8:08 AM, Ben Skeggs <skeggsb at gmail.com> wrote:
> On Tue, Feb 17, 2015 at 5:48 PM, Alexandre Courbot <acourbot at nvidia.com> wrote:
>> instmem for GK20A is allocated using dma_alloc_coherent(), which
>> provides us with a coherent CPU mapping that we never use because
>> instmem objects are accessed through PRAMIN. Switch to
>> dma_alloc_attrs() which gives us the option to dismiss that CPU mapping
>> and free up some CPU virtual space.
>>
>> Signed-off-by: Alexandre Courbot <acourbot at nvidia.com>
>> ---
>>  drm/nouveau/nvkm/subdev/instmem/gk20a.c | 24 ++++++++++++++++++++----
>>  lib/include/nvif/os.h                   | 31 +++++++++++++++++++++++++++++++
>>  2 files changed, 51 insertions(+), 4 deletions(-)
>>
>> diff --git a/drm/nouveau/nvkm/subdev/instmem/gk20a.c b/drm/nouveau/nvkm/subdev/instmem/gk20a.c
>> index 6176f5072496..4c8af6e3677c 100644
>> --- a/drm/nouveau/nvkm/subdev/instmem/gk20a.c
>> +++ b/drm/nouveau/nvkm/subdev/instmem/gk20a.c
>> @@ -24,6 +24,10 @@
>>  #include <core/mm.h>
>>  #include <core/device.h>
>>
>> +#ifdef __KERNEL__
>> +#include <linux/dma-attrs.h>
>> +#endif
>> +
>>  #include "priv.h"
>>
>>  struct gk20a_instobj_priv {
>> @@ -34,6 +38,7 @@ struct gk20a_instobj_priv {
>>         struct nvkm_mem _mem;
>>         void *cpuaddr;
>>         dma_addr_t handle;
>> +       struct dma_attrs attrs;
>>         struct nvkm_mm_node r;
>>  };
>>
>> @@ -91,8 +96,8 @@ gk20a_instobj_dtor(struct nvkm_object *object)
>>         if (unlikely(!node->handle))
>>                 return;
>>
>> -       dma_free_coherent(dev, node->mem->size << PAGE_SHIFT, node->cpuaddr,
>> -                         node->handle);
>> +       dma_free_attrs(dev, node->mem->size << PAGE_SHIFT, node->cpuaddr,
>> +                      node->handle, &node->attrs);
>>
>>         nvkm_instobj_destroy(&node->base);
>>  }
>> @@ -126,8 +131,19 @@ gk20a_instobj_ctor(struct nvkm_object *parent, struct nvkm_object *engine,
>>
>>         node->mem = &node->_mem;
>>
>> -       node->cpuaddr = dma_alloc_coherent(dev, npages << PAGE_SHIFT,
>> -                                          &node->handle, GFP_KERNEL);
>> +       init_dma_attrs(&node->attrs);
>> +       /*
>> +        * We will access this memory through PRAMIN and thus do not need a
>> +        * consistent CPU pointer
>> +        */
>> +       dma_set_attr(DMA_ATTR_NON_CONSISTENT, &node->attrs);
>> +       dma_set_attr(DMA_ATTR_WEAK_ORDERING, &node->attrs);
>> +       dma_set_attr(DMA_ATTR_WRITE_COMBINE, &node->attrs);
>> +       dma_set_attr(DMA_ATTR_NO_KERNEL_MAPPING, &node->attrs);
> I wonder, is it possible to have a per-priv version of this instead of
> per-object?  The kernel's function prototypes aren't marked const or
> anything, which gives me some doubts, but it's worth checking.

I checked the ARM implementation of the DMA API and it seems to be
safe indeed - I will do this. Thanks!