On Thu, 7 Jan 2021 22:17:15 +0100 Marc Kleine-Budde wrote: > > +struct __packed tcan4x5x_buf_cmd { > > + u8 cmd; > > + __be16 addr; > > + u8 len; > > +}; > > This has to be packed, as I assume the compiler would add some space after the > "u8 cmd" to align the __be16 naturally. Ack, packing this one makes sense. > > +struct __packed tcan4x5x_map_buf { > > + struct tcan4x5x_buf_cmd cmd; > > + u8 data[256 * sizeof(u32)]; > > +} ____cacheline_aligned; > > Due to the packing of the struct tcan4x5x_buf_cmd it should have a length of 4 > bytes. Without __packed, will the "u8 data" come directly after the cmd? Yup, u8 with no alignment attribute will follow the previous field with no holes.