Re: [PATCH v9 3/7] ata: libahci: allow to use multiple PHYs

["Antoine Ténart" <antoine.tenart@free-electrons.com>]

Hi Tejun,

On Tue, Jul 08, 2014 at 05:40:10PM -0400, Tejun Heo wrote:
> Hey,
> 
> On Tue, Jul 08, 2014 at 07:49:00PM +0200, Antoine Ténart wrote:
> > > So, yeah, it's being used both as input and output and we also have
> > > the arguments which affect port_map, right?  It does seem confusing.
> > 
> > I do see priv->port_map as being automatically set and then restricted
> > if needed by the port_map input here. I don't see how that's confusing.
> > The only modification is we restrict the port_map parameter to the set
> > of available ports. The port_map argument affected priv->port_map before
> > this patch.
> 
> It is confusing.  If you wanna pass around available ports in hpriv,
> please add a separate field and replace the arguments to
> save_initial_config().

I don't get it. Which argument should I replace in
save_initial_config()? The change is we compute hpriv->port_map.
I don't see which arguments we can add or replace.

If that's more clear, the modification here is equivalent to (when using
the new bindings):

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 40ea583d3610..f9d3cfd5d1bd 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -513,7 +513,7 @@ void ahci_save_initial_config(struct device *dev,
        /* record values to use during operation */
        hpriv->cap = cap;
        hpriv->cap2 = cap2;
-       hpriv->port_map = port_map;
+       hpriv->port_map &= port_map;
 
        if (!hpriv->start_engine)
                hpriv->start_engine = ahci_start_engine;

It just use the argument port_map on the real set of ports. If that's
still not clear, I can add a separate field. But the field will store
the exact same information as hpriv->port_map. We will have something
like:

if (hpriv->available_port_map)
	hpriv->port_map &= hpriv->available_port_map;

> > > Well, so does clk.  Let's say clk is more restricted and phy can be
> > > one or more per port and thus needs to be dynamic.  If so, shouldn't
> > > we at least have some correlation between phys and ports?  It bothers
> > > me that now libahci is carrying random number of resources that it has
> > > no idea how to associate with the ports it manages.  What if later we
> > > want to involve phy driver in power managing unoccupied ports?
> > 
> > I see. This is a first (working) attempt to have a one node per port. I
> > agree that would be nice to have a correlation between ports and PHYs.
> > This can definitively be added when needed without changing the dt
> > bindings as only the internal representation changes. This would also
> > require to get all phys from the port nodes, which is again internal
> > stuff.
> > 
> > Don't you think we can go by steps, and have a following up series for
> > this when needed (like in a power managing series for unoccupied ports)?
> 
> I don't know.  It isn't exactly difficult to make it per-port, is it?
> We already have ahci_port_priv and wouldn't the code actually be
> simpler that way?

I had a quick look on this, and it does not seems to be that simple. The
ahci_port_priv is stored inside the ata_port struct and not accessible
(as of now) from the ahci_host_priv one. The ahci_port_priv is
initialized at the end of ahci_platform_init_host(), far after we need
it. This requires quite a lot of changes. Or is there another way?

To be honest, we are now at v9 and it's been quite a long time since v1.
I'd really like it to be merged in 3.17. As I see it, this patch keeps
the same logic as what was in place before, only with more PHYs.

Don't take me wrong, I really think this is a good idea to have a
per-port PHY information. But this is a refactoring not clearly related
to this series as the logic is not changed. This definitively can be the
subject of a dedicated series, especially if I got it right and the
required modifications are not that obvious.

What do you think?

Thanks,

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com