drm: tweak drm_print_bits()

There is little reason for the from/to logic, printing a subset of
the bits can be done by simply shifting/masking value if needed.

Also use for_each_set_bit().
Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Sean Paul <sean@poorly.run>
Link: http://patchwork.freedesktop.org/patch/msgid/20190923065814.4797-1-kraxel@redhat.com

drivers/gpu/drm/drm_gem_ttm_helper.c

@@ -23,7 +23,7 @@
 void drm_gem_ttm_print_info(struct drm_printer *p, unsigned int indent,
 			    const struct drm_gem_object *gem)
 {
-	static const char const *plname[] = {
+	static const char * const plname[] = {
 		[ TTM_PL_SYSTEM ] = "system",
 		[ TTM_PL_TT     ] = "tt",
 		[ TTM_PL_VRAM   ] = "vram",
@@ -40,7 +40,7 @@ void drm_gem_ttm_print_info(struct drm_printer *p, unsigned int indent,
 	const struct ttm_buffer_object *bo = drm_gem_ttm_of_gem(gem);
 
 	drm_printf_indent(p, indent, "placement=");
-	drm_print_bits(p, bo->mem.placement, plname, 0, ARRAY_SIZE(plname));
+	drm_print_bits(p, bo->mem.placement, plname, ARRAY_SIZE(plname));
 	drm_printf(p, "\n");
 
 	if (bo->mem.bus.is_iomem) {

drivers/gpu/drm/drm_print.c

@@ -189,28 +189,26 @@ EXPORT_SYMBOL(drm_printf);
  * drm_print_bits - print bits to a &drm_printer stream
  *
  * Print bits (in flag fields for example) in human readable form.
- * The first name in the @bits array is for the bit indexed by @from.
  *
  * @p: the &drm_printer
  * @value: field value.
  * @bits: Array with bit names.
- * @from: start of bit range to print (inclusive).
- * @to: end of bit range to print (exclusive).
+ * @nbits: Size of bit names array.
  */
-void drm_print_bits(struct drm_printer *p,
-		    unsigned long value, const char *bits[],
-		    unsigned int from, unsigned int to)
+void drm_print_bits(struct drm_printer *p, unsigned long value,
+		    const char * const bits[], unsigned int nbits)
 {
 	bool first = true;
 	unsigned int i;
 
-	for (i = from; i < to; i++) {
-		if (!(value & (1 << i)))
-			continue;
-		if (WARN_ON_ONCE(!bits[i-from]))
+	if (WARN_ON_ONCE(nbits > BITS_PER_TYPE(value)))
+		nbits = BITS_PER_TYPE(value);
+
+	for_each_set_bit(i, &value, nbits) {
+		if (WARN_ON_ONCE(!bits[i]))
 			continue;
 		drm_printf(p, "%s%s", first ? "" : ",",
-			   bits[i-from]);
+			   bits[i]);
 		first = false;
 	}
 	if (first)

include/drm/drm_print.h

@@ -89,9 +89,8 @@ __printf(2, 3)
 void drm_printf(struct drm_printer *p, const char *f, ...);
 void drm_puts(struct drm_printer *p, const char *str);
 void drm_print_regset32(struct drm_printer *p, struct debugfs_regset32 *regset);
-void drm_print_bits(struct drm_printer *p,
-		    unsigned long value, const char *bits[],
-		    unsigned int from, unsigned int to);
+void drm_print_bits(struct drm_printer *p, unsigned long value,
+		    const char * const bits[], unsigned int nbits);
 
 __printf(2, 0)
 /**