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

From: "Russell King (Oracle)" <[email-masked]>
Date: Thu, 16 Mar 2023 23:10:03 +0000

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 <[email-masked]>
> ---
> 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?

-- 
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