Re: [PATCH 09/10] i2c: i801: Improve register_dell_lis3lv02d_i2c_device

[Heiner Kallweit <hkallweit1@gmail.com>]

On 05.08.2021 16:23, Jean Delvare wrote:
> On Sun, 01 Aug 2021 16:23:34 +0200, Heiner Kallweit wrote:
>> - Use an initializer for struct i2c_board_info info
>> - Use dmi_match()
>> - Simplify loop logic
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  drivers/i2c/busses/i2c-i801.c | 28 +++++++++-------------------
>>  1 file changed, 9 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
>> index 958b2e14b..1ca92a1e0 100644
>> --- a/drivers/i2c/busses/i2c-i801.c
>> +++ b/drivers/i2c/busses/i2c-i801.c
>> @@ -1245,28 +1245,18 @@ static const struct {
>>  
>>  static void register_dell_lis3lv02d_i2c_device(struct i801_priv *priv)
>>  {
>> -	struct i2c_board_info info;
>> -	const char *dmi_product_name;
>> +	struct i2c_board_info info = { .type = "lis3lv02d" };
> 
> Can it be moved to the inner loop where it is used, so that
> initialization only takes place when needed? I don't know how the
> compiler handles that, to be honest.
> 
>>  	int i;
>>  
>> -	dmi_product_name = dmi_get_system_info(DMI_PRODUCT_NAME);
>> -	for (i = 0; i < ARRAY_SIZE(dell_lis3lv02d_devices); ++i) {
>> -		if (strcmp(dmi_product_name,
>> -			   dell_lis3lv02d_devices[i].dmi_product_name) == 0)
>> -			break;
>> -	}
>> -
>> -	if (i == ARRAY_SIZE(dell_lis3lv02d_devices)) {
>> -		dev_warn(&priv->pci_dev->dev,
>> -			 "Accelerometer lis3lv02d is present on SMBus but its"
>> -			 " address is unknown, skipping registration\n");
>> -		return;
>> -	}
>> +	for (i = 0; i < ARRAY_SIZE(dell_lis3lv02d_devices); ++i)
> 
> Outer block without curly braces is discouraged for readability and
> maintenance reasons (see Documentation/process/coding-style.rst section
> 3).
> 
>> +		if (dmi_match(DMI_PRODUCT_NAME, dell_lis3lv02d_devices[i].dmi_product_name)) {
> 
> This causes dmi_get_system_info(DMI_PRODUCT_NAME) to be called for
> every iteration of the loop, slowing down the lookup. It's an exported
> function so it can't be inlined by the compiler. I know this happens
> only once, but we try to keep boot times as short as possible.
> 
I'm aware of this. However we just talk about a small in-memory operation and
the performance impact should be neglectable. dmi_get_system_info() is just
the following:

const char *dmi_get_system_info(int field)
{
	return dmi_ident[field];
}
EXPORT_SYMBOL(dmi_get_system_info);

I'd rate the simpler and better maintainable code higher.
But that's just a personal opinion and mileage may vary.


>> +			info.addr = dell_lis3lv02d_devices[i].i2c_addr;
>> +			i2c_new_client_device(&priv->adapter, &info);
>> +			return;
>> +		}
>>  
>> -	memset(&info, 0, sizeof(struct i2c_board_info));
>> -	info.addr = dell_lis3lv02d_devices[i].i2c_addr;
>> -	strlcpy(info.type, "lis3lv02d", I2C_NAME_SIZE);
>> -	i2c_new_client_device(&priv->adapter, &info);
>> +	pci_warn(priv->pci_dev,
>> +		 "Accelerometer lis3lv02d is present on SMBus but its address is unknown, skipping registration\n");
>>  }
>>  
>>  /* Register optional slaves */
> 
>