Re: [PATCH net-next v3 03/13] net: phy: phy_caps: Move phy_speeds to phy_caps

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Russell,

On Fri, 28 Feb 2025 16:10:35 +0000
"Russell King (Oracle)" <linux@armlinux.org.uk> wrote:

> On Fri, Feb 28, 2025 at 03:55:28PM +0100, Maxime Chevallier wrote:
> > Use the newly introduced link_capabilities array to derive the list of
> > possible speeds when given a combination of linkmodes. As
> > link_capabilities is indexed by speed, we don't have to iterate the
> > whole phy_settings array.
> > 
> > Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

[...]

> > +/**
> > + * phy_caps_speeds() - Fill an array of supported SPEED_* values for given modes
> > + * @speeds: Output array to store the speeds list into
> > + * @size: Size of the output array
> > + * @linkmodes: Linkmodes to get the speeds from
> > + *
> > + * Fills the speeds array with all possible speeds that can be achieved with
> > + * the specified linkmodes.
> > + *
> > + * Returns: The number of speeds filled into the array. If the input array isn't
> > + *	    big enough to store all speeds, fill it as much as possible.
> > + */
> > +size_t phy_caps_speeds(unsigned int *speeds, size_t size,
> > +		       unsigned long *linkmodes)
> > +{
> > +	size_t count;
> > +	int capa;
> > +
> > +	for (capa = 0, count = 0; capa < __LINK_CAPA_MAX && count < size; capa++) {
> > +		if (linkmode_intersects(link_caps[capa].linkmodes, linkmodes) &&
> > +		    (count == 0 || speeds[count - 1] != link_caps[capa].speed))
> > +			speeds[count++] = link_caps[capa].speed;
> > +	}  
> 
> Having looked at several of these patches, there's a common pattern
> emerging, which is we're walking over link_caps in either ascending
> speed order or descending speed order. So I wonder whether it would
> make sense to have:
> 
> #define for_each_link_caps_asc_speed(cap) \
> 	for (cap = link_caps; cap < &link_caps[__LINK_CAPA_MAX]; cap++)
> #define for_each_link_caps_desc_speed(cap) \
> 	for (cap = &link_caps[__LINK_CAPA_MAX - 1]; cap >= link_caps; cap--)
> 
> for where iterating over in speed order is important. E.g. this would
> make the above:
> 
> 	struct link_capabilities *lcap;
> 
> 	for_each_link_caps_asc_speed(lcap)
> 		if (linkmode_intersects(lcap->linkmodes, linkmodes) &&
> 		    (count == 0 || speeds[count - 1] != lcap->speed)) {
> 			speeds[count++] = lcap->speed;
> 			if (count >= size)
> 				break;
> 		}
> 
> which helps to make it explicit that speeds[] is in ascending value
> order.

That makes a lot of sense indeed, I will definitely add that.

Thanks a lot for the review,

Maxime