IB/qib: Eliminate divide/mod in converting idx to egr buf pointer

The context init now saves a shift from rcvegrbufs_perchunk
rcvegrbufs_perchunk_shift using ilog2.   A BUG_ON() protects the
power of 2 assumption.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/qib/qib.h

@@ -171,7 +171,9 @@ struct qib_ctxtdata {
 	/* how many alloc_pages() chunks in rcvegrbuf_pages */
 	u32 rcvegrbuf_chunks;
 	/* how many egrbufs per chunk */
-	u32 rcvegrbufs_perchunk;
+	u16 rcvegrbufs_perchunk;
+	/* ilog2 of above */
+	u16 rcvegrbufs_perchunk_shift;
 	/* order for rcvegrbuf_pages */
 	size_t rcvegrbuf_size;
 	/* rcvhdrq size (for freeing) */
@@ -940,7 +942,9 @@ struct qib_devdata {
 	/* chip address space used by 4k pio buffers */
 	u32 align4k;
 	/* size of each rcvegrbuffer */
-	u32 rcvegrbufsize;
+	u16 rcvegrbufsize;
+	/* log2 of above */
+	u16 rcvegrbufsize_shift;
 	/* localbus width (1, 2,4,8,16,32) from config space  */
 	u32 lbus_width;
 	/* localbus speed in MHz */

drivers/infiniband/hw/qib/qib_driver.c

@@ -279,10 +279,10 @@ int qib_set_linkstate(struct qib_pportdata *ppd, u8 newstate)
  */
 static inline void *qib_get_egrbuf(const struct qib_ctxtdata *rcd, u32 etail)
 {
-	const u32 chunk = etail / rcd->rcvegrbufs_perchunk;
-	const u32 idx =  etail % rcd->rcvegrbufs_perchunk;
+	const u32 chunk = etail >> rcd->rcvegrbufs_perchunk_shift;
+	const u32 idx =  etail & ((u32)rcd->rcvegrbufs_perchunk - 1);
 
-	return rcd->rcvegrbuf[chunk] + idx * rcd->dd->rcvegrbufsize;
+	return rcd->rcvegrbuf[chunk] + (idx << rcd->dd->rcvegrbufsize_shift);
 }
 
 /*

drivers/infiniband/hw/qib/qib_iba6120.c

@@ -3273,6 +3273,8 @@ static int init_6120_variables(struct qib_devdata *dd)
 	/* we always allocate at least 2048 bytes for eager buffers */
 	ret = ib_mtu_enum_to_int(qib_ibmtu);
 	dd->rcvegrbufsize = ret != -1 ? max(ret, 2048) : QIB_DEFAULT_MTU;
+	BUG_ON(!is_power_of_2(dd->rcvegrbufsize));
+	dd->rcvegrbufsize_shift = ilog2(dd->rcvegrbufsize);
 
 	qib_6120_tidtemplate(dd);
 

drivers/infiniband/hw/qib/qib_iba7220.c

@@ -4085,6 +4085,8 @@ static int qib_init_7220_variables(struct qib_devdata *dd)
 	/* we always allocate at least 2048 bytes for eager buffers */
 	ret = ib_mtu_enum_to_int(qib_ibmtu);
 	dd->rcvegrbufsize = ret != -1 ? max(ret, 2048) : QIB_DEFAULT_MTU;
+	BUG_ON(!is_power_of_2(dd->rcvegrbufsize));
+	dd->rcvegrbufsize_shift = ilog2(dd->rcvegrbufsize);
 
 	qib_7220_tidtemplate(dd);
 

drivers/infiniband/hw/qib/qib_iba7322.c

@@ -6205,6 +6205,8 @@ static int qib_init_7322_variables(struct qib_devdata *dd)
 
 	/* we always allocate at least 2048 bytes for eager buffers */
 	dd->rcvegrbufsize = max(mtu, 2048);
+	BUG_ON(!is_power_of_2(dd->rcvegrbufsize));
+	dd->rcvegrbufsize_shift = ilog2(dd->rcvegrbufsize);
 
 	qib_7322_tidtemplate(dd);
 

drivers/infiniband/hw/qib/qib_init.c

@@ -183,6 +183,9 @@ struct qib_ctxtdata *qib_create_ctxtdata(struct qib_pportdata *ppd, u32 ctxt)
 		rcd->rcvegrbuf_chunks = (rcd->rcvegrcnt +
 			rcd->rcvegrbufs_perchunk - 1) /
 			rcd->rcvegrbufs_perchunk;
+		BUG_ON(!is_power_of_2(rcd->rcvegrbufs_perchunk));
+		rcd->rcvegrbufs_perchunk_shift =
+			ilog2(rcd->rcvegrbufs_perchunk);
 	}
 	return rcd;
 }