netdev - Re: [RFC PATCH] phylib: mdio: handle register/unregister/register sequence

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Message-ID: <521610FE.7080807@overkiz.com>
Date:	Thu, 22 Aug 2013 15:24:14 +0200
From:	boris brezillon <b.brezillon@...rkiz.com>
To:	Florian Fainelli <f.fainelli@...il.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Mark Brown <broonie@...nel.org>,
	Nick Bowler <nbowler@...iptictech.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH] phylib: mdio: handle register/unregister/register
 sequence

On 22/08/2013 15:15, Florian Fainelli wrote:
> 2013/8/22 boris brezillon <b.brezillon@...rkiz.com>:
>> Hello Florian,
>>
>> Thanks for your answer.
>>
>>
>> On 22/08/2013 14:43, Florian Fainelli wrote:
>>> Hello Boris,
>>>
>>> 2013/8/22 Boris BREZILLON <b.brezillon@...rkiz.com>:
>>>> Hello,
>>>>
>>>> This patch is a proposal to support the register/unregister/register
>>>> sequence on a given mdio bus.
>>>>
>>>> I use the register/unregister/register sequence to add a fallback when
>>>> the
>>>> of_mdiobus_register (this function calls mdiobus_register with phy_mask
>>>> set to ~0) does not register any phy device (because the device tree does
>>>> not define any phy).
>>>> In this case I call mdiobus_unregister and then call mdiobus_register
>>>> with
>>>> a phy_mask set to 0 to trigger a full mdio bus scan.
>>>>
>>>> I'm not sure this is the right way to do it (this is why I added RFC in
>>>> the
>>>> subject).
>>>>
>>>> Could someone help me figuring out what I should use to implement my
>>>> fallback ?
>>>>
>>>> 1) use the register/unregister/register sequence
>>>> 2) reimplement the "for (i = 0; i < PHY_MAX_ADDR; i++)" mdiobus_scan loop
>>> I think solution 2 is nicer, in that case, would it be enough in your
>>> case to export a function called mdiobus_scan()? You could call at a
>>> time you know PHY devices have a chance of having been probed?
>> mdiobus_scan is already exported:
>> struct phy_device *mdiobus_scan(struct mii_bus *bus, int addr);
>>
>> This function scans the presence of a phy device at a given address.
>>
>> What I need is a loop which scan all the possible address on the given
>> mdio bus:
>>
>> struct phy_device *mdiobus_full_scan(struct mii_bus *bus)
>> {
>>      int i;
>>      for (i = 0; i < PHY_MAX_ADDR; i++) {
>>          if ((bus->phy_mask & (1 << i)) == 0) {
>>              struct phy_device *phydev;
>>
>>              phydev = mdiobus_scan(bus, i);
>>              if (IS_ERR(phydev)) {
>>                  err = PTR_ERR(phydev);
>>                  goto error;
>>              }
>>          }
>>      }
>>      return 0;
>>
>> error:
>>      while (--i >= 0) {
>>
>>          if (bus->phy_map[i])
>>              device_unregister(&bus->phy_map[i]->dev);
>>      }
>> }
>> EXPORT_SYMBOL(mdiobus_full_scan);
>>
>> Since I am the only one who need this kind of functionnality right now, I'm
>> not sure
>> this is a good idea to export a new function.
> A possible other use case for this full-scan is when you do not detect
> a PHY connected to your MDIO bus, and that you did not register a
> fixed PHY early enough for it to have been scanned by the fixed MDIO
> bus emulation. In that case the driver may:
>
> - scan hardware MDIO bus
> - do not find any PHY, register a fixed PHY
> - trigger a fixed MDIO bus full-rescan
> - attach to the discovered fixed PHY
>
> this is something currently done by the TI CPMAC driver in
> drivers/net/ethernet/ti/cpmac.c (altough fixed_phy_add() is called
> from platform code).
>

Okay, then we should consider this option.

>> This behaviour may be implemented in the of_mdiobus_register function:
>> when no dt phy node are found in the mdio bus dt node, we could launch a
>> full
>> scan.
>>
>> What do you think ?
> There is an existing kind of "autoscan" feature in
> drivers/of/of_mdio.c, starting with the second foreach_child_node()
> loop, so maybe that specific part could be exported and would achieve
> what you are looking for? It relies on the Ethernet PHY nodes to be
> attached to the MDIO bus node, but I assume this is what ultimately
> happens in your case as well?

The second foreach_child_node loop only registers the dt phy nodes
which does not define any reg property (automatic address asssignement ?).

Indeed, what I need is a fallback when the device tree does not define 
any phy
device (for old device tree backward compatibility).

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