linux-kernel - Re: [PATCH] ethtool: changes of emac_regs structure accordingly within driver emac

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Message-ID: <1433182286.6319.183.camel@decadent.org.uk>
Date:	Mon, 01 Jun 2015 19:11:26 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Ivan Mikhaylov <ivan@...ibm.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] ethtool: changes of emac_regs structure accordingly
 within driver emac_regs structure.

On Mon, 2015-06-01 at 16:30 +0400, Ivan Mikhaylov wrote:
> On Mon, 1 June 2015 12:57 +0400
> Ben Hutchings <ben@...adent.org.uk> wrote:
> 
> >On Thu, 2015-05-21 at 19:09 +0400, Ivan Mikhaylov wrote:
> >> In ibm_emac.c in ethtool size of emac structure which passing through
> >> to driver is nailed down and not correlating with current emac_regs
> >> structure.
> >> 
> >> Signed-off-by: Ivan Mikhaylov <ivan@...ibm.com>
> >[...]
> >
> >This is not backward-compatible.  It ought to be possible to mix and
> >match old and new ethtool and driver, except for the EMAC4SYNC case
> >which has been broken up until now.
> >
> >Using the new definition of struct emac_regs, I think the driver and
> >ethtool need to agree that the MAC register dump sizes are:
> >
> >EMAC:      offsetof(struct emac_regs, u1)
> >EMAC4:     offsetof(struct emac_regs, u1.emac4) + sizeof(p->u1.emac4)
> >EMAC4SYNC: offsetof(struct emac_regs, u1.emac4sync) +
> >sizeof(p->u1.emac4sync)
> >
> >Ben.
> >
> >-- 
> >Ben Hutchings
> >Reality is just a crutch for people who can't handle science fiction.
> 
> Actually it is backward-compatible because we don't care about size
> which is coming from driver side, only what we doing is map of driver
> structure to ethtool structure and results will be same
> for emac and emac4.
> 
>  struct emac_regs *p = (struct emac_regs *)(hdr + 1);

The following registers won't be printed correctly.

> Also size which you mentioned (112 emac, 116 emac4) can be different
> from what you saying cause this managed by dts files where we can set
> something like 0x100 or 0x80 for this memory area and we will still
> have problem in representing MII area if this size wasn't set right
> in dts.

Yes, I understand that.  However, the in-tree device trees consistently
use those as the resource sizes so I think ethtool used to work properly
for the machines supported by those.  Increasing the size of the MAC
register dump is a regression for them.

Ben.

> Ethtool will be work in same way even if we have emac or emac4.
> 
> Thank you for respond!
> 

-- 
Ben Hutchings
Power corrupts.  Absolute power is kind of neat.
                           - John Lehman, Secretary of the US Navy 1981-1987

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