Simplify padding calculations.
1. Taking the remainder of a binary value when
the divisor is a power of two, such as,
a % 2^n is identical to, a & (2^n - 1) in base-2
arithmetic, and so expressions like this:
(12 - (lower_32_bits(ring->wptr) & 7)) % 8
are superflous. And can be reduced to a single
remainder-taking operation.
2. Subtracting the remainder modulo 8 out of 12
and then again taking the remainder modulo 8,
yields the same result as simply subtracting
the value out of 4 and then taking the remainder.
This is true because 4 belongs to the congruence
(residue) class {4 + 8*k}, k in Z. (So using,
{..., -12, -4, 4, 12, 20, ...}, would yield
the same final result.
So the above expression, becomes,
(4 - lower_32_bits(ring->wptr)) & 7
3. Now since 8 is part of the conguence class
{0 + 8*k}, k in Z, and from 1) and 2) above, then,
(8 - (ib->length_dw & 0x7)) % 8
becomes, simply,
(-ib->length_dw) & 7.
This patch implements all of the above in this code.
v2: Comment update and spacing.
v3: Add 1, 2, 3, above, in this commit message.
Signed-off-by: Luben Tuikov <luben.tuikov@xxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/cik_sdma.c | 4 ++--
drivers/gpu/drm/amd/amdgpu/sdma_v2_4.c | 4 ++--
drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c | 4 ++--
drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c | 4 ++--
drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c | 17 ++++++++++++-----
5 files changed, 20 insertions(+), 13 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/cik_sdma.c b/drivers/gpu/drm/amd/amdgpu/cik_sdma.c
index 1f22a8d0f7f3..4274ccf765de 100644
--- a/drivers/gpu/drm/amd/amdgpu/cik_sdma.c
+++ b/drivers/gpu/drm/amd/amdgpu/cik_sdma.c
@@ -228,7 +228,7 @@ static void cik_sdma_ring_emit_ib(struct amdgpu_ring *ring,
u32 extra_bits = vmid & 0xf;
/* IB packet must end on a 8 DW boundary */
- cik_sdma_ring_insert_nop(ring, (12 - (lower_32_bits(ring->wptr) & 7)) % 8);
+ cik_sdma_ring_insert_nop(ring, (4 - lower_32_bits(ring->wptr)) & 7);
amdgpu_ring_write(ring, SDMA_PACKET(SDMA_OPCODE_INDIRECT_BUFFER, 0, extra_bits));
amdgpu_ring_write(ring, ib->gpu_addr & 0xffffffe0); /* base must be 32 byte aligned */
@@ -811,7 +811,7 @@ static void cik_sdma_ring_pad_ib(struct amdgpu_ring *ring, struct amdgpu_ib *ib)
u32 pad_count;
int i;
- pad_count = (8 - (ib->length_dw & 0x7)) % 8;
+ pad_count = (-ib->length_dw) & 7;
for (i = 0; i < pad_count; i++)
if (sdma && sdma->burst_nop && (i == 0))
ib->ptr[ib->length_dw++] =
diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v2_4.c b/drivers/gpu/drm/amd/amdgpu/sdma_v2_4.c
index 606b621145a1..fd7fa6082563 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v2_4.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v2_4.c
@@ -255,7 +255,7 @@ static void sdma_v2_4_ring_emit_ib(struct amdgpu_ring *ring,
unsigned vmid = AMDGPU_JOB_GET_VMID(job);
/* IB packet must end on a 8 DW boundary */
- sdma_v2_4_ring_insert_nop(ring, (10 - (lower_32_bits(ring->wptr) & 7)) % 8);
+ sdma_v2_4_ring_insert_nop(ring, (2 - lower_32_bits(ring->wptr)) & 7);
amdgpu_ring_write(ring, SDMA_PKT_HEADER_OP(SDMA_OP_INDIRECT) |
SDMA_PKT_INDIRECT_HEADER_VMID(vmid & 0xf));
@@ -750,7 +750,7 @@ static void sdma_v2_4_ring_pad_ib(struct amdgpu_ring *ring, struct amdgpu_ib *ib
u32 pad_count;
int i;
- pad_count = (8 - (ib->length_dw & 0x7)) % 8;
+ pad_count = (-ib->length_dw) & 7;
for (i = 0; i < pad_count; i++)
if (sdma && sdma->burst_nop && (i == 0))
ib->ptr[ib->length_dw++] =
diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c b/drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c
index a559573ec8fd..4a8a7f0f3a9c 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c
@@ -429,7 +429,7 @@ static void sdma_v3_0_ring_emit_ib(struct amdgpu_ring *ring,
unsigned vmid = AMDGPU_JOB_GET_VMID(job);
/* IB packet must end on a 8 DW boundary */
- sdma_v3_0_ring_insert_nop(ring, (10 - (lower_32_bits(ring->wptr) & 7)) % 8);
+ sdma_v3_0_ring_insert_nop(ring, (2 - lower_32_bits(ring->wptr)) & 7);
amdgpu_ring_write(ring, SDMA_PKT_HEADER_OP(SDMA_OP_INDIRECT) |
SDMA_PKT_INDIRECT_HEADER_VMID(vmid & 0xf));
@@ -1021,7 +1021,7 @@ static void sdma_v3_0_ring_pad_ib(struct amdgpu_ring *ring, struct amdgpu_ib *ib
u32 pad_count;
int i;
- pad_count = (8 - (ib->length_dw & 0x7)) % 8;
+ pad_count = (-ib->length_dw) & 7;
for (i = 0; i < pad_count; i++)
if (sdma && sdma->burst_nop && (i == 0))
ib->ptr[ib->length_dw++] =
diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c b/drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c
index bd9ed33bab43..c69df0cb21ec 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c
@@ -698,7 +698,7 @@ static void sdma_v4_0_ring_emit_ib(struct amdgpu_ring *ring,
unsigned vmid = AMDGPU_JOB_GET_VMID(job);
/* IB packet must end on a 8 DW boundary */
- sdma_v4_0_ring_insert_nop(ring, (10 - (lower_32_bits(ring->wptr) & 7)) % 8);
+ sdma_v4_0_ring_insert_nop(ring, (2 - lower_32_bits(ring->wptr)) & 7);
amdgpu_ring_write(ring, SDMA_PKT_HEADER_OP(SDMA_OP_INDIRECT) |
SDMA_PKT_INDIRECT_HEADER_VMID(vmid & 0xf));
@@ -1579,7 +1579,7 @@ static void sdma_v4_0_ring_pad_ib(struct amdgpu_ring *ring, struct amdgpu_ib *ib
u32 pad_count;
int i;
- pad_count = (8 - (ib->length_dw & 0x7)) % 8;
+ pad_count = (-ib->length_dw) & 7;
for (i = 0; i < pad_count; i++)
if (sdma && sdma->burst_nop && (i == 0))
ib->ptr[ib->length_dw++] =
diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c b/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
index 119364293cec..3912937f878f 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
@@ -382,8 +382,15 @@ static void sdma_v5_0_ring_emit_ib(struct amdgpu_ring *ring,
unsigned vmid = AMDGPU_JOB_GET_VMID(job);
uint64_t csa_mc_addr = amdgpu_sdma_get_csa_mc_addr(ring, vmid);
- /* IB packet must end on a 8 DW boundary */
- sdma_v5_0_ring_insert_nop(ring, (10 - (lower_32_bits(ring->wptr) & 7)) % 8);
+ /* An IB packet must end on a 8 DW boundary--the next dword
+ * must be on a 8-dword boundary. Our IB packet below is 6
+ * dwords long, thus add x number of NOPs, such that, in
+ * modular arithmetic,
+ * wptr + 6 + x = 8k, k >= 0, which in C is,
+ * (wptr + 6 + x) % 8 = 0.
+ * The expression below, is a solution of x.
+ */
+ sdma_v5_0_ring_insert_nop(ring, (2 - lower_32_bits(ring->wptr)) & 7);
amdgpu_ring_write(ring, SDMA_PKT_HEADER_OP(SDMA_OP_INDIRECT) |
SDMA_PKT_INDIRECT_HEADER_VMID(vmid & 0xf));
@@ -1076,10 +1083,10 @@ static void sdma_v5_0_vm_set_pte_pde(struct amdgpu_ib *ib,
}
/**
- * sdma_v5_0_ring_pad_ib - pad the IB to the required number of dw
- *
+ * sdma_v5_0_ring_pad_ib - pad the IB
* @ib: indirect buffer to fill with padding
*
+ * Pad the IB with NOPs to a boundary multiple of 8.
*/
static void sdma_v5_0_ring_pad_ib(struct amdgpu_ring *ring, struct amdgpu_ib *ib)
{
@@ -1087,7 +1094,7 @@ static void sdma_v5_0_ring_pad_ib(struct amdgpu_ring *ring, struct amdgpu_ib *ib
u32 pad_count;
int i;
- pad_count = (8 - (ib->length_dw & 0x7)) % 8;
+ pad_count = (-ib->length_dw) & 0x7;
for (i = 0; i < pad_count; i++)
if (sdma && sdma->burst_nop && (i == 0))
ib->ptr[ib->length_dw++] =
--
2.24.0.390.g083378cc35
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