Improve comments and doc for ECP
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 04a557b..07ed110 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -310,9 +310,15 @@
* MBEDTLS_ERR_ECP_IN_PROGRESS will be returned by the
* function performing the computation. It is then the
* caller's responsibility to either call again with the same
- * arguments until it returns 0 or an error code; or to free
+ * parameters until it returns 0 or an error code; or to free
* the restart context if the operation is to be aborted.
*
+ * It is strictly required that all input parameters and the
+ * restart context be the same on successive calls for the
+ * same operation, but output parameters need not be the
+ * same; they must not be used until the function finally
+ * returns 0.
+ *
* This only affects functions that accept a pointer to a
* \c mbedtls_ecp_restart_ctx as an argument, and only works
* if that pointer valid (in particular, not NULL).
@@ -334,10 +340,13 @@
* operations, and will do so even if max_ops is set to a
* lower value. That minimum depends on the curve size, and
* can be made lower by decreasing the value of
- * \c MBEDTLS_ECP_WINDOW_SIZE. As an indication, with that
- * parameter set to 4, the minimum amount of blocking is:
- * - around 165 basic operations for P-256
- * - around 330 basic operations for P-384
+ * \c MBEDTLS_ECP_WINDOW_SIZE. As an indication, here is the
+ * lowest effective value for various curves and values of
+ * that parameter (w for short):
+ * w=6 w=5 w=4 w=3 w=2
+ * P-256 208 208 160 136 124
+ * P-384 682 416 320 272 248
+ * P-521 1364 832 640 544 496
*
* \note This setting is currently ignored by Curve25519
*/