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From: Grant Likely <grant.likely@secretlab.ca>
Date: Tue, 9 Feb 2010 18:53:01 -0700
Message-ID: <fa686aa41002091753n36c59e3brd2b2174035e4933d@mail.gmail.com>
Subject: Re: [PATCH] [V3] net: emaclite: adding MDIO and phy lib support
To: John Linn <John.Linn@xilinx.com>
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Cc: linuxppc-dev@ozlabs.org, netdev@vger.kernel.org,
	Sadanand Mutyala <sadanan@xilinx.com>, jgarzik@pobox.com,
	John Williams <john.williams@petalogix.com>
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On Tue, Feb 9, 2010 at 4:00 PM, John Linn <John.Linn@xilinx.com> wrote:
>> -----Original Message-----
>> From: John Williams [mailto:john.williams@petalogix.com]
>> Sent: Tuesday, February 09, 2010 3:30 PM
>> To: John Linn
>> Cc: netdev@vger.kernel.org; linuxppc-dev@ozlabs.org; jgarzik@pobox.com; =
grant.likely@secretlab.ca;
>> jwboyer@linux.vnet.ibm.com; Sadanand Mutyala
>> Subject: Re: [PATCH] [V3] net: emaclite: adding MDIO and phy lib support
>>
>> Hi John,
>>
>> Sorry If I'm painting bike-sheds here, just one tiny tweak might be in
>> order to standardise your mutex_unlock exit path:
>>
>> > +static int xemaclite_mdio_read(struct mii_bus *bus, int phy_id, int r=
eg)
>> > +{
>> > + =A0 =A0 =A0 struct net_local *lp =3D bus->priv;
>> > + =A0 =A0 =A0 u32 ctrl_reg;
>> > + =A0 =A0 =A0 u32 rc;
>> > +
>> > + =A0 =A0 =A0 mutex_lock(&lp->mdio_mutex);
>> > +
>> > + =A0 =A0 =A0 if (xemaclite_mdio_wait(lp)) {
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 mutex_unlock(&lp->mdio_mutex);
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -ETIMEDOUT;
>> > + =A0 =A0 =A0 }
>>
>> [snip]
>>
>>
>> > + =A0 =A0 =A0 if (xemaclite_mdio_wait(lp)) {
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 mutex_unlock(&lp->mdio_mutex);
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -ETIMEDOUT;
>> > + =A0 =A0 =A0 }
>>
>> [snip]
>>
>>
>> > + =A0 =A0 =A0 dev_dbg(&lp->ndev->dev,
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 "xemaclite_mdio_read(phy_id=3D%i, reg=3D=
%x) =3D=3D %x\n",
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 phy_id, reg, rc);
>> > +
>> > + =A0 =A0 =A0 return rc;
>>
>> Can this be better expressed like this:
>>
>> my_func() {
>> =A0 mutex_lock()
>> ..
>>
>> =A0 if(some error) {
>> =A0 =A0 rc=3D-ETIMEDOUT;
>> =A0 =A0 goto out_unlock;
>> =A0 }
>> =A0 ...
>>
>> =A0 /* success path */
>> =A0 rc=3D0;
>> ..
>> out_unlock:
>> =A0 mutex_unlock()
>> =A0 return rc;
>> }
>>
>>
>> Is this style still favoured in driver exit paths?
>
> It looks to me like the mutex is not needed in the driver mdio functions =
as there's a mutex in the mdiobus functions already.

Yes, you're correct, but you still need to protect against direct
calls to the read/write routines from within the driver.  But you can
probably use the mdio_lock mutex for this.

g.