linux-kernel - Re: [PATCH net V2] net: stmmac: Fix for mismatched host/device DMA address width

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Message-ID: <ZBOhy02DFBlnIQR1@shell.armlinux.org.uk>
Date:   Thu, 16 Mar 2023 23:10:03 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Jochen Henneberg <jh@...neberg-systemdesign.com>
Cc:     netdev@...r.kernel.org,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Wong Vee Khee <veekhee@...le.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Revanth Kumar Uppala <ruppala@...dia.com>,
        Andrey Konovalov <andrey.konovalov@...aro.org>,
        Tan Tee Min <tee.min.tan@...ux.intel.com>,
        Voon Weifeng <weifeng.voon@...el.com>,
        Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net V2] net: stmmac: Fix for mismatched host/device DMA
 address width

On Thu, Mar 16, 2023 at 02:15:03PM +0100, Jochen Henneberg wrote:
> Currently DMA address width is either read from a RO device register
> or force set from the platform data. This breaks DMA when the host DMA
> address width is <=32it but the device is >32bit.
> 
> Right now the driver may decide to use a 2nd DMA descriptor for
> another buffer (happens in case of TSO xmit) assuming that 32bit
> addressing is used due to platform configuration but the device will
> still use both descriptor addresses as one address.
> 
> This can be observed with the Intel EHL platform driver that sets
> 32bit for addr64 but the MAC reports 40bit. The TX queue gets stuck in
> case of TCP with iptables NAT configuration on TSO packets.
> 
> The logic should be like this: Whatever we do on the host side (memory
> allocation GFP flags) should happen with the host DMA width, whenever
> we decide how to set addresses on the device registers we must use the
> device DMA address width.
> 
> This patch renames the platform address width field from addr64 (term
> used in device datasheet) to host_addr and uses this value exclusively
> for host side operations while all chip operations consider the device
> DMA width as read from the device register.
> 
> Fixes: 7cfc4486e7ea ("stmmac: intel: Configure EHL PSE0 GbE and PSE1 GbE to 32 bits DMA addressing")
> Signed-off-by: Jochen Henneberg <jh@...neberg-systemdesign.com>
> ---
> V2: Fixes from checkpatch.pl for commit message
> 
>  drivers/net/ethernet/stmicro/stmmac/common.h  |  1 +
>  .../net/ethernet/stmicro/stmmac/dwmac-imx.c   |  2 +-
>  .../net/ethernet/stmicro/stmmac/dwmac-intel.c |  4 +--
>  .../ethernet/stmicro/stmmac/dwmac-mediatek.c  |  2 +-
>  .../net/ethernet/stmicro/stmmac/stmmac_main.c | 30 ++++++++++---------
>  include/linux/stmmac.h                        |  2 +-
>  6 files changed, 22 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/common.h b/drivers/net/ethernet/stmicro/stmmac/common.h
> index 6b5d96bced47..55a728b1b708 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/common.h
> +++ b/drivers/net/ethernet/stmicro/stmmac/common.h
> @@ -418,6 +418,7 @@ struct dma_features {
>  	unsigned int frpbs;
>  	unsigned int frpes;
>  	unsigned int addr64;
> +	unsigned int host_addr;

Obvious question: is host_addr an address? From the above description it
sounds like this is more of a host address width indicator.

Maybe call these "dev_addr_width" and "host_addr_width" so it's clear
what each of these are?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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