gpu: nvgpu: Add characterstics field to expose max ctxsw ring buffer size

NVGPU_CTXSW_IOCTL_RING_SETUP can be used to setup a custom ring buffer
and it accepts size via arguments. nvgpu driver will return an error
if size requested is greater than 128 * 4096 but this value is hardcoded
and not exposed anywhere.
Add characteristics field in nvgpu.h to expose this size so that corresponding
nvrm_gpu API can use it.

Bug 2169674

Change-Id: Icf9465d4eec6ba3a307ea9490bd5da563944e4f6
Signed-off-by: Anup Mahindre <amahindre@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1967596
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/gk20a/gr_gk20a.h

@@ -393,6 +393,7 @@ struct gr_gk20a {
 	struct gk20a_cs_snapshot	*cs_data;
 #endif
 	u32 max_css_buffer_size;
+	u32 max_ctxsw_ring_buffer_size;
 };
 
 void gk20a_fecs_dump_falcon_stats(struct gk20a *g);

drivers/gpu/nvgpu/os/linux/ctxsw_trace.c

@@ -580,6 +580,8 @@ int gk20a_ctxsw_trace_init(struct gk20a *g)
 	if (unlikely(err))
 		goto fail;
 
+	g->gr.max_ctxsw_ring_buffer_size = GK20A_CTXSW_TRACE_MAX_VM_RING_SIZE;
+
 	return 0;
 
 fail:

drivers/gpu/nvgpu/os/linux/ioctl_ctrl.c

@@ -326,6 +326,7 @@ gk20a_ctrl_ioctl_gpu_characteristics(
 	gpu.sm_arch_warp_count = g->params.sm_arch_warp_count;
 
 	gpu.max_css_buffer_size = g->gr.max_css_buffer_size;
+	gpu.max_ctxsw_ring_buffer_size = g->gr.max_ctxsw_ring_buffer_size;
 
 	gpu.gpu_ioctl_nr_last = NVGPU_GPU_IOCTL_LAST;
 	gpu.tsg_ioctl_nr_last = NVGPU_TSG_IOCTL_LAST;

include/uapi/linux/nvgpu.h

@@ -283,6 +283,9 @@ struct nvgpu_gpu_characteristics {
 	__s16 ctxsw_ioctl_nr_last;
 	__u8 reserved2[6];
 
+	__u32 max_ctxsw_ring_buffer_size;
+	__u32 reserved3;
+
 	/* Notes:
 	   - This struct can be safely appended with new fields. However, always
 	     keep the structure size multiple of 8 and make sure that the binary