On Tue, Aug 11, 2020 at 09:11:41PM +0200, Bartosz Golaszewski wrote:

On Sun, Aug 9, 2020 at 3:26 PM Kent Gibson [off-list ref] wrote:

quoted

[snip]

quoted

+/*
+ * Maximum number of requested lines.
+ *
+ * Must be no greater than 64 as bitmaps are limited to 64-bits, and a
+ * multiple of 2 to ensure 32/64-bit alignment of structs.
+ */
+#define GPIO_V2_LINES_MAX 64
+

If we refer to bitmaps for which helpers are defined in
include/linux/bitmap.h then they're not limited to 64-bits. I'd just
say here that we want to fit into 64-bit integers for simplicity.

Strictly speaking, userspace doesn't know about include/linux/bitmap.h,
but I'm happy to remove any ambiguity.

Does this work for you?:

 * Must be no greater than 64, as bitmaps are restricted here to 64-bits
 * for simplicity, and a multiple of 2 to ensure 32/64-bit alignment of
 * structs.

Cheers,
Kent.