* [PATCH] drm/amd/display: avoid 64-bit division
@ 2019-07-08 13:52 Arnd Bergmann
[not found] ` <DM6PR12MB320967C48957C4F2F0E92438FEF10@DM6PR12MB3209.namprd12.prod.outlook.com>
0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2019-07-08 13:52 UTC (permalink / raw)
To: Harry Wentland, Leo Li, Alex Deucher, Christian König,
David (ChunMing) Zhou, David Airlie, Daniel Vetter
Cc: Arnd Bergmann, Chris Park, Charlene Liu, Jun Lei, Tony Cheng,
Bhawanpreet Lakha, Tony Cheng, Anthony Koo, David Francis,
Dmytro Laktyushkin, Nikola Cornij, amd-gfx, dri-devel,
linux-kernel
On 32-bit architectures, dividing a 64-bit integer in the kernel
leads to a link error:
ERROR: "__udivdi3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: "__divdi3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
Change the two recently introduced instances to a multiply+shift
operation that is also much cheaper on 32-bit architectures.
We can do that here, since both of them are really 32-bit numbers
that change a few percent.
Fixes: bedbbe6af4be ("drm/amd/display: Move link functions from dc to dc_link")
Fixes: f18bc4e53ad6 ("drm/amd/display: update calculated bounding box logic for NV")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/gpu/drm/amd/display/dc/core/dc_link.c | 4 ++--
drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index c17db5c144aa..8dbf759eba45 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -3072,8 +3072,8 @@ uint32_t dc_link_bandwidth_kbps(
* but the difference is minimal and is in a safe direction,
* which all works well around potential ambiguity of DP 1.4a spec.
*/
- long long fec_link_bw_kbps = link_bw_kbps * 970LL;
- link_bw_kbps = (uint32_t)(fec_link_bw_kbps / 1000LL);
+ link_bw_kbps = mul_u64_u32_shr(BIT_ULL(32) * 970LL / 1000,
+ link_bw_kbps, 32);
}
#endif
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 b35327bafbc5..70ac8a95d2db 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
@@ -2657,7 +2657,7 @@ static void update_bounding_box(struct dc *dc, struct _vcs_dpi_soc_bounding_box_
calculated_states[i].dram_speed_mts = uclk_states[i] * 16 / 1000;
// FCLK:UCLK ratio is 1.08
- min_fclk_required_by_uclk = ((unsigned long long)uclk_states[i]) * 1080 / 1000000;
+ min_fclk_required_by_uclk = mul_u64_u32_shr(BIT_ULL(32) * 1080 / 1000000, uclk_states[i], 32);
calculated_states[i].fabricclk_mhz = (min_fclk_required_by_uclk < min_dcfclk) ?
min_dcfclk : min_fclk_required_by_uclk;
--
2.20.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] drm/amd/display: avoid 64-bit division
[not found] ` <BN6PR12MB1809956A9C61870CB7F675F5F7F10@BN6PR12MB1809.namprd12.prod.outlook.com>
@ 2019-07-09 19:37 ` Arnd Bergmann
0 siblings, 0 replies; 2+ messages in thread
From: Arnd Bergmann @ 2019-07-09 19:37 UTC (permalink / raw)
To: Deucher, Alexander
Cc: Abramov, Slava, Wentland, Harry, Li, Sun peng (Leo),
Koenig, Christian, Zhou, David(ChunMing),
David Airlie, Daniel Vetter, Liu, Charlene, Park, Chris, Cheng,
Tony, Francis, David, linux-kernel, amd-gfx, Cornij, Nikola,
Laktyushkin, Dmytro, dri-devel, Lei, Jun, Lakha, Bhawanpreet,
Koo, Anthony
On Tue, Jul 9, 2019 at 6:40 PM Deucher, Alexander
<Alexander.Deucher@amd.com> wrote:
>
> I'll just apply Arnd's patch. If the display team wants to adjust it later to clarify the
> operation, they should go ahead as a follow up patch.
Thanks!
> From: Abramov, Slava
> Sent: Tuesday, July 9, 2019 12:31 PM
> > Thanks for bisecting this issue.
> >
> > I wonder whether you are going to commit your patch or planning to update it and it's
> > still in your work queue. We have one of our 32-bit builds failing because of this
> > issue, so that I would like either to fix it or wait to your fix if it has chances to go
> > upstream today.
I was going to update the patch, but had not gotten to that yet.
Arnd
^ permalink raw reply [flat|nested] 2+ messages in thread
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2019-07-08 13:52 [PATCH] drm/amd/display: avoid 64-bit division Arnd Bergmann
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