Re: [PATCH net-next v4 5/8] mfd: zl3073x: Add functions to work with register mailboxes

[Andrew Lunn]

On Thu, Apr 24, 2025 at 09:53:39PM +0200, Ivan Vecera wrote:
> 
> 
> On 24. 04. 25 9:18 odp., Andrew Lunn wrote:
> > > During taking 613cbb91e9ce ("media: Add MIPI CCI register access helper
> > > functions") approach I found they are using for these functions u64
> > > regardless of register size... Just to accommodate the biggest
> > > possible value. I know about weakness of 'void *' usage but u64 is not
> > > also ideal as the caller is forced to pass always 8 bytes for reading
> > > and forced to reserve 8 bytes for each read value on stack.
> > 
> > In this device, how are the u48s used? Are they actually u48s, or are
> > they just u8[6], for example a MAC address? The network stack has lots
> > of functions like:
> > 
> > eth_hw_addr_set(struct net_device *dev, const u8 *addr)
> 
> u48 registers always represent 48bit integer... they read from device using
> bulk read as big-endian 48bit int. The same is valid also for u16
> and u32.

Then a u64 makes sense, plus on write to hardware a check the upper
bits are 0. These u48s are going to be stored in a u64 anyway, since C
does not have a u48 type.

But all the other types do exist in C, so you should use them and have
type checking.

	Andrew