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

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Jochen Henneberg <jh@henneberg-systemdesign.com>
Cc: netdev@vger.kernel.org,
	Giuseppe Cavallaro <peppe.cavallaro@st.com>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>,
	Jose Abreu <joabreu@synopsys.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	Wong Vee Khee <veekhee@apple.com>,
	Kurt Kanzenbach <kurt@linutronix.de>,
	Revanth Kumar Uppala <ruppala@nvidia.com>,
	Andrey Konovalov <andrey.konovalov@linaro.org>,
	Tan Tee Min <tee.min.tan@linux.intel.com>,
	Voon Weifeng <weifeng.voon@intel.com>,
	Mohammad Athari Bin Ismail <mohammad.athari.ismail@intel.com>,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org
Subject: Re: [PATCH net V2] net: stmmac: Fix for mismatched host/device DMA address width
Date: Thu, 16 Mar 2023 23:10:03 +0000	[thread overview]
Message-ID: <ZBOhy02DFBlnIQR1@shell.armlinux.org.uk> (raw)
In-Reply-To: <20230316131503.738933-1-jh@henneberg-systemdesign.com>

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@henneberg-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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