Re: [PATCH] amdgpu: Avoid sleeping during FPU critical sections

[Christian König]

Am 11.01.21 um 17:32 schrieb Daniel Vetter:
> On Mon, Jan 11, 2021 at 09:53:56AM +0100, Christian König wrote:
> > Am 08.01.21 um 22:58 schrieb Jeremy Cline:
> > > dcn20_resource_construct() includes a number of kzalloc(GFP_KERNEL)
> > > calls which can sleep, but kernel_fpu_begin() disables preemption and
> > > sleeping in this context is invalid.
> > >
> > > The only places the FPU appears to be required is in the
> > > init_soc_bounding_box() function and when calculating the
> > > {min,max}_fill_clk_mhz. Narrow the scope to just these two parts to
> > > avoid sleeping while using the FPU.
> > >
> > > Fixes: 7a8a3430be15 ("amdgpu: Wrap FPU dependent functions in dc20")
> > > Cc: Timothy Pearson <tpearson@xxxxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Jeremy Cline <jcline@xxxxxxxxxx>
> > Good catch, but I would rather replace the kzalloc(GFP_KERNEL) with a
> > kzalloc(GFP_ATOMIC) for now.
> >
> > We have tons of problems with this DC_FP_START()/DC_FP_END() annotations and
> > are even in the process of moving them out of the file because the compiles
> > tend to clutter FP registers even outside of the annotated ranges on some
> > architectures.
> Out of curiosity, what's the plan? Soft-fp implementation for DC so you
> can keep the algorithms all unchanged, or redoing them as some fixed point
> with careful review and retesting everything? Something else?

My last status is that we want to move all FP related functions into a 
separate C file.

Then compile only that file with FP enabled and all callers of those 
functions must protected the function calls with FP enable/disable.

That's the only way we can guarantee that no FP state is corrupted.

Regards,
Christian.

> -Daniel
>
> > Regards,
> > Christian.
> >
> > > ---
> > >    drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c | 8 ++++----
> > >    1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
> > > index e04ecf0fc0db..a4fa5bf016c1 100644
> > > --- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
> > > +++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
> > > @@ -3622,6 +3622,7 @@ static bool init_soc_bounding_box(struct dc *dc,
> > >    	if (bb && ASICREV_IS_NAVI12_P(dc->ctx->asic_id.hw_internal_rev)) {
> > >    		int i;
> > > +		DC_FP_START();
> > >    		dcn2_0_nv12_soc.sr_exit_time_us =
> > >    				fixed16_to_double_to_cpu(bb->sr_exit_time_us);
> > >    		dcn2_0_nv12_soc.sr_enter_plus_exit_time_us =
> > > @@ -3721,6 +3722,7 @@ static bool init_soc_bounding_box(struct dc *dc,
> > >    			dcn2_0_nv12_soc.clock_limits[i].dram_speed_mts =
> > >    					fixed16_to_double_to_cpu(bb->clock_limits[i].dram_speed_mts);
> > >    		}
> > > +		DC_FP_END();
> > >    	}
> > >    	if (pool->base.pp_smu) {
> > > @@ -3777,8 +3779,6 @@ static bool dcn20_resource_construct(
> > >    	enum dml_project dml_project_version =
> > >    			get_dml_project_version(ctx->asic_id.hw_internal_rev);
> > > -	DC_FP_START();
> > > -
> > >    	ctx->dc_bios->regs = &bios_regs;
> > >    	pool->base.funcs = &dcn20_res_pool_funcs;
> > > @@ -3959,8 +3959,10 @@ static bool dcn20_resource_construct(
> > >    				ranges.reader_wm_sets[i].wm_inst = i;
> > >    				ranges.reader_wm_sets[i].min_drain_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MIN;
> > >    				ranges.reader_wm_sets[i].max_drain_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MAX;
> > > +				DC_FP_START();
> > >    				ranges.reader_wm_sets[i].min_fill_clk_mhz = (i > 0) ? (loaded_bb->clock_limits[i - 1].dram_speed_mts / 16) + 1 : 0;
> > >    				ranges.reader_wm_sets[i].max_fill_clk_mhz = loaded_bb->clock_limits[i].dram_speed_mts / 16;
> > > +				DC_FP_END();
> > >    				ranges.num_reader_wm_sets = i + 1;
> > >    			}
> > > @@ -4125,12 +4127,10 @@ static bool dcn20_resource_construct(
> > >    		pool->base.oem_device = NULL;
> > >    	}
> > > -	DC_FP_END();
> > >    	return true;
> > >    create_fail:
> > > -	DC_FP_END();
> > >    	dcn20_resource_destruct(pool);
> > >    	return false;