RE: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties into MDIO nodes

[Dylan Hung <dylan_hung@aspeedtech.com>]

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@lunn.ch]
> Sent: 2022年3月22日 11:01 AM
> To: Dylan Hung <dylan_hung@aspeedtech.com>
> Cc: Krzysztof Kozlowski <krzk@kernel.org>; robh+dt@kernel.org;
> joel@jms.id.au; andrew@aj.id.au; hkallweit1@gmail.com;
> linux@armlinux.org.uk; davem@davemloft.net; kuba@kernel.org;
> pabeni@redhat.com; p.zabel@pengutronix.de; devicetree@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linux-aspeed@lists.ozlabs.org;
> linux-kernel@vger.kernel.org; netdev@vger.kernel.org; BMC-SW
> <BMC-SW@aspeedtech.com>; stable@vger.kernel.org
> Subject: Re: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties into MDIO
> nodes
> 
> On Tue, Mar 22, 2022 at 02:32:13AM +0000, Dylan Hung wrote:
> > > -----Original Message-----
> > > From: Krzysztof Kozlowski [mailto:krzk@kernel.org]
> > > Sent: 2022年3月21日 11:53 PM
> > > To: Dylan Hung <dylan_hung@aspeedtech.com>; robh+dt@kernel.org;
> > > joel@jms.id.au; andrew@aj.id.au; andrew@lunn.ch;
> > > hkallweit1@gmail.com; linux@armlinux.org.uk; davem@davemloft.net;
> > > kuba@kernel.org; pabeni@redhat.com; p.zabel@pengutronix.de;
> > > devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> > > linux-aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org;
> > > netdev@vger.kernel.org
> > > Cc: BMC-SW <BMC-SW@aspeedtech.com>; stable@vger.kernel.org
> > > Subject: Re: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties
> > > into MDIO nodes
> > >
> > > On 21/03/2022 10:56, Dylan Hung wrote:
> > > > Add reset control properties into MDIO nodes.  The 4 MDIO
> > > > controllers in
> > > > AST2600 SOC share one reset control bit SCU50[3].
> > > >
> > > > Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
> > > > Cc: stable@vger.kernel.org
> > >
> > > Please describe the bug being fixed. See stable-kernel-rules.
> >
> > Thank you for your comment.
> > The reset deassertion of the MDIO device was usually done by the
> bootloader (u-boot).
> > However, one of our clients uses proprietary bootloader and doesn't
> > deassert the MDIO reset so failed to access the HW in kernel driver.
> 
> So are you saying mainline u-boot releases the reset?
> 
Yes, if the mdio devices are used in u-boot.

> > The reset deassertion is missing in the kernel driver since it was
> > created, should I add a BugFix for the first commit of this driver?
> 
> Yes, that is normal. Ideally the kernel should not depend on u-boot, because
> often people want to use other bootloaders, e.g. barebox. You should also
> consider kexec, where one kernel hands over to another kernel, without the
> bootloader being involved. In such a situation, you ideally want to assert and
> deassert the reset just to clean away any state the old kernel left around.
> 
> But please do note, that the reset is optional, since you need to be able to
> work with old DT blobs which don't have the reset property in them.
> 

Thank you. I will let the reset property be optional and modify the error-checking
in the driver accordingly in V3.


> 	Andrew
> 
>