netdev - Re: [PATCH v1 net-next] e1000e: Remove duplicated writel() in e1000_configure

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Message-ID: <b6b56dd0-b6ff-47d1-a678-d2fde5184723@lunn.ch>
Date: Wed, 4 Sep 2024 14:13:38 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Takamitsu Iwai <takamitz@...zon.co.jp>
Cc: anthony.l.nguyen@...el.com, davem@...emloft.net, edumazet@...gle.com,
	intel-wired-lan@...ts.osuosl.org, kuba@...nel.org,
	netdev@...r.kernel.org, pabeni@...hat.com,
	przemyslaw.kitszel@...el.com
Subject: Re: [PATCH v1 net-next] e1000e: Remove duplicated writel() in
 e1000_configure_tx/rx()

On Wed, Sep 04, 2024 at 02:56:46PM +0900, Takamitsu Iwai wrote:
> > So you have confirmed with the datsheet that the write is not needed?
> >
> > As i said, this is a hardware register, not memory. Writes are not
> > always idempotent. It might be necessary to write it twice.
> 
> I have checked following datasheets and I can not find that we need to write
> RDH, RDT, TDH, TDT registers twice at initialization.
> 
> https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/82577-gbe-phy-datasheet.pdf
> https://www.intel.com/content/www/us/en/content-details/613460/intel-82583v-gbe-controller-datasheet.html
> 
> Write happened once before commit 0845d45e900c, so just out of curiosity,
> have you seen such a device?

This is just risk minimisation. I don't want e1000e to be broken
because you removed a write. I'm trying to ensure you fully understand
what you are changing, and have verified it is a safe change. I don't
have this hardware, so i cannot test it.

> My colleague, Kohei, tested the patch with a real hardware and will provide his
> Tested-by shortly.

Please resend the patch, adding his Tested-by: and update the commit
message to summarise this discussion. Explain how you determined this
is safe.

Thanks
	Andrew