nfp: bpf: support unaligned read offset

This patch add the support for unaligned read offset, i.e. the read offset
to the start of packet cache area is not aligned to REG_WIDTH. In this
case, the read area might across maximum three transfer-in registers.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -553,6 +553,19 @@ wrp_reg_subpart(struct nfp_prog *nfp_prog, swreg dst, swreg src, u8 field_len,
 	emit_ld_field_any(nfp_prog, dst, mask, src, sc, offset * 8, true);
 }
 
+/* wrp_reg_or_subpart() - load @field_len bytes from low end of @src, or the
+ * result to @dst from offset, there is no change on the other bits of @dst.
+ */
+static void
+wrp_reg_or_subpart(struct nfp_prog *nfp_prog, swreg dst, swreg src,
+		   u8 field_len, u8 offset)
+{
+	enum shf_sc sc = offset ? SHF_SC_L_SHF : SHF_SC_NONE;
+	u8 mask = ((1 << field_len) - 1) << offset;
+
+	emit_ld_field(nfp_prog, dst, mask, src, sc, 32 - offset * 8);
+}
+
 static void
 addr40_offset(struct nfp_prog *nfp_prog, u8 src_gpr, swreg offset,
 	      swreg *rega, swreg *regb)
@@ -1864,6 +1877,60 @@ mem_ldx_data_init_pktcache(struct nfp_prog *nfp_prog,
 		     off, xfer_num - 1, true, indir);
 }
 
+static int
+mem_ldx_data_from_pktcache_unaligned(struct nfp_prog *nfp_prog,
+				     struct nfp_insn_meta *meta,
+				     unsigned int size)
+{
+	s16 range_start = meta->pkt_cache.range_start;
+	s16 insn_off = meta->insn.off - range_start;
+	swreg dst_lo, dst_hi, src_lo, src_mid;
+	u8 dst_gpr = meta->insn.dst_reg * 2;
+	u8 len_lo = size, len_mid = 0;
+	u8 idx = insn_off / REG_WIDTH;
+	u8 off = insn_off % REG_WIDTH;
+
+	dst_hi = reg_both(dst_gpr + 1);
+	dst_lo = reg_both(dst_gpr);
+	src_lo = reg_xfer(idx);
+
+	/* The read length could involve as many as three registers. */
+	if (size > REG_WIDTH - off) {
+		/* Calculate the part in the second register. */
+		len_lo = REG_WIDTH - off;
+		len_mid = size - len_lo;
+
+		/* Calculate the part in the third register. */
+		if (size > 2 * REG_WIDTH - off)
+			len_mid = REG_WIDTH;
+	}
+
+	wrp_reg_subpart(nfp_prog, dst_lo, src_lo, len_lo, off);
+
+	if (!len_mid) {
+		wrp_immed(nfp_prog, dst_hi, 0);
+		return 0;
+	}
+
+	src_mid = reg_xfer(idx + 1);
+
+	if (size <= REG_WIDTH) {
+		wrp_reg_or_subpart(nfp_prog, dst_lo, src_mid, len_mid, len_lo);
+		wrp_immed(nfp_prog, dst_hi, 0);
+	} else {
+		swreg src_hi = reg_xfer(idx + 2);
+
+		wrp_reg_or_subpart(nfp_prog, dst_lo, src_mid,
+				   REG_WIDTH - len_lo, len_lo);
+		wrp_reg_subpart(nfp_prog, dst_hi, src_mid, len_lo,
+				REG_WIDTH - len_lo);
+		wrp_reg_or_subpart(nfp_prog, dst_hi, src_hi, REG_WIDTH - len_lo,
+				   len_lo);
+	}
+
+	return 0;
+}
+
 static int
 mem_ldx_data_from_pktcache_aligned(struct nfp_prog *nfp_prog,
 				   struct nfp_insn_meta *meta,
@@ -1900,10 +1967,10 @@ mem_ldx_data_from_pktcache(struct nfp_prog *nfp_prog,
 {
 	u8 off = meta->insn.off - meta->pkt_cache.range_start;
 
-	if (WARN_ON_ONCE(!IS_ALIGNED(off, REG_WIDTH)))
-		return -EOPNOTSUPP;
-
+	if (IS_ALIGNED(off, REG_WIDTH))
 		return mem_ldx_data_from_pktcache_aligned(nfp_prog, meta, size);
+
+	return mem_ldx_data_from_pktcache_unaligned(nfp_prog, meta, size);
 }
 
 static int