On 2021/3/19 14:35, Viresh Kumar wrote:> On 19-03-21, 14:29, Jie Deng wrote:
>> I also see example drivers/i2c/busses/i2c-xiic.c. Some people might
think
>> this way is more clearer than
>>
>> updating each member in probe. Basically, I think it's just a
matter of
>> personal preference which doesn't
> Memory used by one instance of struct i2c_adapter (on arm64):
>
> struct i2c_adapter {
> struct module * owner; /* 0 8 */
> unsigned int class; /* 8 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> const struct i2c_algorithm * algo; /* 16 8 */
> void * algo_data; /* 24 8 */
> const struct i2c_lock_operations * lock_ops; /* 32 8 */
> struct rt_mutex bus_lock; /* 40 32 */
> /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
> struct rt_mutex mux_lock; /* 72 32 */
> int timeout; /* 104 4 */
> int retries; /* 108 4 */
> struct device dev; /* 112 744 */
>
> /* XXX last struct has 7 bytes of padding */
>
> /* --- cacheline 13 boundary (832 bytes) was 24 bytes ago --- */
> long unsigned int locked_flags; /* 856 8 */
> int nr; /* 864 4 */
> char name[48]; /* 868 48 */
>
> /* XXX 4 bytes hole, try to pack */
>
> /* --- cacheline 14 boundary (896 bytes) was 24 bytes ago --- */
> struct completion dev_released; /* 920 32 */
> struct mutex userspace_clients_lock; /* 952 32
*/
> /* --- cacheline 15 boundary (960 bytes) was 24 bytes ago --- */
> struct list_head userspace_clients; /* 984 16 */
> struct i2c_bus_recovery_info * bus_recovery_info; /* 1000 8
*/
> const struct i2c_adapter_quirks * quirks; /* 1008 8 */
> struct irq_domain * host_notify_domain; /* 1016 8 */
> /* --- cacheline 16 boundary (1024 bytes) --- */
>
> /* size: 1024, cachelines: 16, members: 19 */
> /* sum members: 1016, holes: 2, sum holes: 8 */
> /* paddings: 1, sum paddings: 7 */
> };
>
> So, this extra instance that i2c-xiic.c is creating (and that you want to
> create) is going to waste 1KB of memory and it will never be used.
>
> This is bad coding practice IMHO and it is not really about personal
preference.
I will remove that structure and update the members in probe.