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

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Date:   Tue, 22 Mar 2022 03:22:37 +0000
From:   Dylan Hung <dylan_hung@...eedtech.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Krzysztof Kozlowski <krzk@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        BMC-SW <BMC-SW@...eedtech.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties into MDIO
 nodes

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@...n.ch]
> Sent: 2022年3月22日 11:01 AM
> To: Dylan Hung <dylan_hung@...eedtech.com>
> Cc: Krzysztof Kozlowski <krzk@...nel.org>; robh+dt@...nel.org;
> joel@....id.au; andrew@...id.au; hkallweit1@...il.com;
> linux@...linux.org.uk; davem@...emloft.net; kuba@...nel.org;
> pabeni@...hat.com; p.zabel@...gutronix.de; devicetree@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; linux-aspeed@...ts.ozlabs.org;
> linux-kernel@...r.kernel.org; netdev@...r.kernel.org; BMC-SW
> <BMC-SW@...eedtech.com>; stable@...r.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@...nel.org]
> > > Sent: 2022年3月21日 11:53 PM
> > > To: Dylan Hung <dylan_hung@...eedtech.com>; robh+dt@...nel.org;
> > > joel@....id.au; andrew@...id.au; andrew@...n.ch;
> > > hkallweit1@...il.com; linux@...linux.org.uk; davem@...emloft.net;
> > > kuba@...nel.org; pabeni@...hat.com; p.zabel@...gutronix.de;
> > > devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> > > linux-aspeed@...ts.ozlabs.org; linux-kernel@...r.kernel.org;
> > > netdev@...r.kernel.org
> > > Cc: BMC-SW <BMC-SW@...eedtech.com>; stable@...r.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@...eedtech.com>
> > > > Cc: stable@...r.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
> 
>