[RSLIB] Support non-canonical GF representations

For the CAFÉ NAND controller, we need to support non-canonical 
representations of the Galois field. Allow the caller to provide its own 
function for generating the field, and CAFÉ can use rslib instead of its
own implementation.

Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

2 files changed, 73 insertions, 15 deletions

diff --git a/include/linux/rslib.h b/include/linux/rslib.h
index ace25acfdc97..746580c1939c 100644
--- a/include/linux/rslib.h
+++ b/include/linux/rslib.h
@@ -34,6 +34,7 @@
  * @prim:       Primitive element, index form
  * @iprim:      prim-th root of 1, index form
  * @gfpoly:     The primitive generator polynominal
+ * @gffunc:     Function to generate the field, if non-canonical representation
  * @users:      Users of this structure
  * @list:       List entry for the rs control list
 */
@@ -48,6 +49,7 @@ struct rs_control {
         int             prim;
         int             iprim;
         int             gfpoly;
+        int             (*gffunc)(int);
         int             users;
         struct list_head list;
 };
@@ -77,6 +79,8 @@ int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
 /* Create or get a matching rs control structure */
 struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
                            int nroots);
+struct rs_control *init_rs_non_canonical(int symsize, int (*func)(int),
+                                         int fcr, int prim, int nroots);
 
 /* Release a rs control structure */
 void free_rs(struct rs_control *rs);
diff --git a/lib/reed_solomon/reed_solomon.c b/lib/reed_solomon/reed_solomon.c
index a4b730a2180c..5b0d8522b7ca 100644
--- a/lib/reed_solomon/reed_solomon.c
+++ b/lib/reed_solomon/reed_solomon.c
@@ -56,6 +56,7 @@ static DEFINE_MUTEX(rslistlock);
  * rs_init - Initialize a Reed-Solomon codec
  * @symsize:    symbol size, bits (1-8)
  * @gfpoly:     Field generator polynomial coefficients
+ * @gffunc:     Field generator function
  * @fcr:        first root of RS code generator polynomial, index form
  * @prim:       primitive element to generate polynomial roots
  * @nroots:     RS code generator polynomial degree (number of roots)
@@ -63,8 +64,8 @@ static DEFINE_MUTEX(rslistlock);
  * Allocate a control structure and the polynom arrays for faster
  * en/decoding. Fill the arrays according to the given parameters.
  */
-static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
-                                   int prim, int nroots)
+static struct rs_control *rs_init(int symsize, int gfpoly, int (*gffunc)(int),
+                                  int fcr, int prim, int nroots)
 {
         struct rs_control *rs;
         int i, j, sr, root, iprim;
@@ -82,6 +83,7 @@ static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
         rs->prim = prim;
         rs->nroots = nroots;
         rs->gfpoly = gfpoly;
+        rs->gffunc = gffunc;
 
         /* Allocate the arrays */
         rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
@@ -99,17 +101,26 @@ static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
         /* Generate Galois field lookup tables */
         rs->index_of[0] = rs->nn;       /* log(zero) = -inf */
         rs->alpha_to[rs->nn] = 0;       /* alpha**-inf = 0 */
-        sr = 1;
-        for (i = 0; i < rs->nn; i++) {
-                rs->index_of[sr] = i;
-                rs->alpha_to[i] = sr;
-                sr <<= 1;
-                if (sr & (1 << symsize))
-                        sr ^= gfpoly;
-                sr &= rs->nn;
+        if (gfpoly) {
+                sr = 1;
+                for (i = 0; i < rs->nn; i++) {
+                        rs->index_of[sr] = i;
+                        rs->alpha_to[i] = sr;
+                        sr <<= 1;
+                        if (sr & (1 << symsize))
+                                sr ^= gfpoly;
+                        sr &= rs->nn;
+                }
+        } else {
+                sr = gffunc(0);
+                for (i = 0; i < rs->nn; i++) {
+                        rs->index_of[sr] = i;
+                        rs->alpha_to[i] = sr;
+                        sr = gffunc(sr);
+                }
         }
         /* If it's not primitive, exit */
-        if(sr != 1)
+        if(sr != rs->alpha_to[0])
                 goto errpol;
 
         /* Find prim-th root of 1, used in decoding */
@@ -173,18 +184,22 @@ void free_rs(struct rs_control *rs)
 }
 
 /**
- * init_rs - Find a matching or allocate a new rs control structure
+ * init_rs_internal - Find a matching or allocate a new rs control structure
  *  @symsize:   the symbol size (number of bits)
  *  @gfpoly:    the extended Galois field generator polynomial coefficients,
  *              with the 0th coefficient in the low order bit. The polynomial
  *              must be primitive;
+ *  @gffunc:    pointer to function to generate the next field element,
+ *              or the multiplicative identity element if given 0.  Used
+ *              instead of gfpoly if gfpoly is 0
  *  @fcr:       the first consecutive root of the rs code generator polynomial
  *              in index form
  *  @prim:      primitive element to generate polynomial roots
  *  @nroots:    RS code generator polynomial degree (number of roots)
  */
-struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
-                           int nroots)
+static struct rs_control *init_rs_internal(int symsize, int gfpoly,
+                                           int (*gffunc)(int), int fcr,
+                                           int prim, int nroots)
 {
         struct list_head        *tmp;
         struct rs_control       *rs;
@@ -208,6 +223,8 @@ struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
                         continue;
                 if (gfpoly != rs->gfpoly)
                         continue;
+                if (gffunc != rs->gffunc)
+                        continue;
                 if (fcr != rs->fcr)
                         continue;
                 if (prim != rs->prim)
@@ -220,7 +237,7 @@ struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
         }
 
         /* Create a new one */
-        rs = rs_init(symsize, gfpoly, fcr, prim, nroots);
+        rs = rs_init(symsize, gfpoly, gffunc, fcr, prim, nroots);
         if (rs) {
                 rs->users = 1;
                 list_add(&rs->list, &rslist);
@@ -230,6 +247,42 @@ out:
         return rs;
 }
 
+/**
+ * init_rs - Find a matching or allocate a new rs control structure
+ *  @symsize:   the symbol size (number of bits)
+ *  @gfpoly:    the extended Galois field generator polynomial coefficients,
+ *              with the 0th coefficient in the low order bit. The polynomial
+ *              must be primitive;
+ *  @fcr:       the first consecutive root of the rs code generator polynomial
+ *              in index form
+ *  @prim:      primitive element to generate polynomial roots
+ *  @nroots:    RS code generator polynomial degree (number of roots)
+ */
+struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
+                           int nroots)
+{
+        return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots);
+}
+
+/**
+ * init_rs_non_canonical - Find a matching or allocate a new rs control
+ *                         structure, for fields with non-canonical
+ *                         representation
+ *  @symsize:   the symbol size (number of bits)
+ *  @gffunc:    pointer to function to generate the next field element,
+ *              or the multiplicative identity element if given 0.  Used
+ *              instead of gfpoly if gfpoly is 0
+ *  @fcr:       the first consecutive root of the rs code generator polynomial
+ *              in index form
+ *  @prim:      primitive element to generate polynomial roots
+ *  @nroots:    RS code generator polynomial degree (number of roots)
+ */
+struct rs_control *init_rs_non_canonical(int symsize, int (*gffunc)(int),
+                                         int fcr, int prim, int nroots)
+{
+        return init_rs_internal(symsize, 0, gffunc, fcr, prim, nroots);
+}
+
 #ifdef CONFIG_REED_SOLOMON_ENC8
 /**
  *  encode_rs8 - Calculate the parity for data values (8bit data width)
@@ -321,6 +374,7 @@ EXPORT_SYMBOL_GPL(decode_rs16);
 #endif
 
 EXPORT_SYMBOL_GPL(init_rs);
+EXPORT_SYMBOL_GPL(init_rs_non_canonical);
 EXPORT_SYMBOL_GPL(free_rs);
 
 MODULE_LICENSE("GPL");