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

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Message-ID: <20240904055646.58588-1-takamitz@amazon.co.jp>
Date: Wed, 4 Sep 2024 14:56:46 +0900
From: Takamitsu Iwai <takamitz@...zon.co.jp>
To: <andrew@...n.ch>
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>, <takamitz@...zon.co.jp>
Subject: Re: [PATCH v1 net-next] e1000e: Remove duplicated writel() in e1000_configure_tx/rx()

> 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?

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