Re: [PATCH 17/18] tty: serial: samsung: shrink port feature flags to u8

Jiri Slaby
2024-01-19T09:55:00Z

Hi,

On 19. 01. 24, 10:43, Tudor Ambarus wrote:
>>> If using unsigned int the bitfied is combined with the previous u8
>>> fields, whereas if using u8 the bitfield will be independently defined.
>>> So no benefit in terms of memory footprint, it's just a cosmetic change
>>> to align the bitfield with the previous u8 fields. Allowing u32 for just
>>> a bit can be misleading as one would ask itself where are the other
>>> bits. Between a u32 bitfield and a bool a u8 bitfield seems like a good
>>> compromise.
>>
>> Why? What's wrong with bool? bitfields have terrible semantics wrt
>> atomic writes for example.
>>
>
> Bool occupies a byte and if more port features will ever be added we'll
> occupy more bytes. Here's how the structure will look like with a bool:
>
> struct s3c24xx_uart_info {
> const char * name; /* 0 8 */
> enum s3c24xx_port_type type; /* 8 4 */
> unsigned int port_type; /* 12 4 */
> unsigned int fifosize; /* 16 4 */
> u32 rx_fifomask; /* 20 4 */
> u32 rx_fifoshift; /* 24 4 */
> u32 rx_fifofull; /* 28 4 */
> u32 tx_fifomask; /* 32 4 */
> u32 tx_fifoshift; /* 36 4 */
> u32 tx_fifofull; /* 40 4 */
> u32 clksel_mask; /* 44 4 */
> u32 clksel_shift; /* 48 4 */
> u32 ucon_mask; /* 52 4 */
> u8 def_clk_sel; /* 56 1 */
> u8 num_clks; /* 57 1 */
> u8 iotype; /* 58 1 */
> bool has_divslot; /* 59 1 */
>
> /* size: 64, cachelines: 1, members: 17 */
> /* padding: 4 */
> };
>
> What's your preference?

bool :).

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