linux-kernel - Re: [PATCH v4 1/1] net: axienet: Move reset before 64-bit DMA detection

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Message-ID: <20230622133204.2ba95c21@kernel.org>
Date:   Thu, 22 Jun 2023 13:32:04 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Maxim Kochetkov <fido_max@...ox.ru>
Cc:     netdev@...r.kernel.org, Robert Hancock <robert.hancock@...ian.com>,
        Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Michal Simek <michal.simek@....com>,
        Andre Przywara <andre.przywara@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] net: axienet: Move reset before 64-bit DMA
 detection

On Thu, 22 Jun 2023 22:22:45 +0300 Maxim Kochetkov wrote:
> 64-bit DMA detection will fail if axienet was started before (by boot
> loader, boot ROM, etc). In this state axienet will not start properly.
> XAXIDMA_TX_CDESC_OFFSET + 4 register (MM2S_CURDESC_MSB) is used to detect
> 64-bit DMA capability here. But datasheet says: When DMACR.RS is 1
> (axienet is in enabled state), CURDESC_PTR becomes Read Only (RO) and
> is used to fetch the first descriptor. So iowrite32()/ioread32() trick
> to this register to detect 64-bit DMA will not work.
> So move axienet reset before 64-bit DMA detection.
> 
> Fixes: f735c40ed93c ("net: axienet: Autodetect 64-bit DMA capability")
> Signed-off-by: Maxim Kochetkov <fido_max@...ox.ru>
> Reviewed-by: Robert Hancock <robert.hancock@...ian.com>
> Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@....com>

Quoting documentation:

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