nfp: bpf: add stack read support

Add simple stack read support, similar to write in every aspect,
but data flowing the other way.  Note that unlike write which can
be done in smaller than word quantities, if registers are loaded
with less-than-word of stack contents - the values have to be
zero extended.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/bpf/jit.c

@@ -644,11 +644,65 @@ data_st_host_order(struct nfp_prog *nfp_prog, u8 dst_gpr, swreg offset,
 
 typedef int
 (*lmem_step)(struct nfp_prog *nfp_prog, u8 gpr, u8 gpr_byte, s32 off,
-	     unsigned int size);
+	     unsigned int size, bool new_gpr);
+
+static int
+wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off,
+	      unsigned int size, bool new_gpr)
+{
+	u32 idx, src_byte;
+	enum shf_sc sc;
+	swreg reg;
+	int shf;
+	u8 mask;
+
+	if (WARN_ON_ONCE(dst_byte + size > 4 || off % 4 + size > 4))
+		return -EOPNOTSUPP;
+
+	idx = off / 4;
+
+	/* Move the entire word */
+	if (size == 4) {
+		wrp_mov(nfp_prog, reg_both(dst), reg_lm(0, idx));
+		return 0;
+	}
+
+	src_byte = off % 4;
+
+	mask = (1 << size) - 1;
+	mask <<= dst_byte;
+
+	if (WARN_ON_ONCE(mask > 0xf))
+		return -EOPNOTSUPP;
+
+	shf = abs(src_byte - dst_byte) * 8;
+	if (src_byte == dst_byte) {
+		sc = SHF_SC_NONE;
+	} else if (src_byte < dst_byte) {
+		shf = 32 - shf;
+		sc = SHF_SC_L_SHF;
+	} else {
+		sc = SHF_SC_R_SHF;
+	}
+
+	/* ld_field can address fewer indexes, if offset too large do RMW.
+	 * Because we RMV twice we waste 2 cycles on unaligned 8 byte writes.
+	 */
+	if (idx <= RE_REG_LM_IDX_MAX) {
+		reg = reg_lm(0, idx);
+	} else {
+		reg = imm_a(nfp_prog);
+		wrp_mov(nfp_prog, reg, reg_lm(0, idx));
+	}
+
+	emit_ld_field_any(nfp_prog, reg_both(dst), mask, reg, sc, shf, new_gpr);
+
+	return 0;
+}
 
 static int
 wrp_lmem_store(struct nfp_prog *nfp_prog, u8 src, u8 src_byte, s32 off,
-	       unsigned int size)
+	       unsigned int size, bool new_gpr)
 {
 	u32 idx, dst_byte;
 	enum shf_sc sc;
@@ -705,12 +759,16 @@ wrp_lmem_store(struct nfp_prog *nfp_prog, u8 src, u8 src_byte, s32 off,
 
 static int
 mem_op_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
-	     unsigned int size, u8 gpr, lmem_step step)
+	     unsigned int size, u8 gpr, bool clr_gpr, lmem_step step)
 {
 	s32 off = nfp_prog->stack_depth + meta->insn.off;
+	u8 prev_gpr = 255;
 	u32 gpr_byte = 0;
 	int ret;
 
+	if (clr_gpr && size < 8)
+		wrp_immed(nfp_prog, reg_both(gpr + 1), 0);
+
 	while (size) {
 		u32 slice_end;
 		u8 slice_size;
@@ -719,10 +777,12 @@ mem_op_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 		slice_end = min(off + slice_size, round_up(off + 1, 4));
 		slice_size = slice_end - off;
 
-		ret = step(nfp_prog, gpr, gpr_byte, off, slice_size);
+		ret = step(nfp_prog, gpr, gpr_byte, off, slice_size,
+			   gpr != prev_gpr);
 		if (ret)
 			return ret;
 
+		prev_gpr = gpr;
 		gpr_byte += slice_size;
 		if (gpr_byte >= 4) {
 			gpr_byte -= 4;
@@ -1232,6 +1292,14 @@ static int data_ind_ld4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 				     meta->insn.src_reg * 2, 4);
 }
 
+static int
+mem_ldx_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
+	      unsigned int size)
+{
+	return mem_op_stack(nfp_prog, meta, size, meta->insn.dst_reg * 2, true,
+			    wrp_lmem_load);
+}
+
 static int mem_ldx_skb(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 		       u8 size)
 {
@@ -1315,6 +1383,9 @@ mem_ldx(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 	if (meta->ptr.type == PTR_TO_PACKET)
 		return mem_ldx_data(nfp_prog, meta, size);
 
+	if (meta->ptr.type == PTR_TO_STACK)
+		return mem_ldx_stack(nfp_prog, meta, size);
+
 	return -EOPNOTSUPP;
 }
 
@@ -1396,7 +1467,7 @@ static int
 mem_stx_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 	      unsigned int size)
 {
-	return mem_op_stack(nfp_prog, meta, size, meta->insn.src_reg * 2,
+	return mem_op_stack(nfp_prog, meta, size, meta->insn.src_reg * 2, false,
 			    wrp_lmem_store);
 }