netdev - Re: [PATCH net] tg3: Set coherent DMA mask bits to 31 for BCM57766 chipsets

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Message-ID: <ZzxywJTKIVm94ep7@localhost.localdomain>
Date: Tue, 19 Nov 2024 12:13:04 +0100
From: Michal Kubiak <michal.kubiak@...el.com>
To: Pavan Chebbi <pavan.chebbi@...adcom.com>
CC: <davem@...emloft.net>, <michael.chan@...adcom.com>, <edumazet@...gle.com>,
	<gospo@...adcom.com>, <kuba@...nel.org>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>, <andrew+netdev@...n.ch>, Salam Noureddine
	<noureddine@...sta.com>, Kalesh AP <kalesh-anakkur.purayil@...adcom.com>,
	Somnath Kotur <somnath.kotur@...adcom.com>
Subject: Re: [PATCH net] tg3: Set coherent DMA mask bits to 31 for BCM57766
 chipsets

On Mon, Nov 18, 2024 at 09:57:41PM -0800, Pavan Chebbi wrote:
> The hardware on Broadcom 1G chipsets have a known limitation
> where they cannot handle DMA addresses that cross over 4GB.
> When such an address is encountered, the hardware sets the
> address overflow error bit in the DMA status register and
> triggers a reset.
> 
> However, BCM57766 hardware is setting the overflow bit and
> triggering a reset in some cases when there is no actual
> underlying address overflow. The hardware team analyzed the
> issue and concluded that it is happening when the status
> block update has an address with higher (b16 to b31) bits
> as 0xffff following a previous update that had lowest bits
> as 0xffff.
> 
> To work around this bug in the BCM57766 hardware, set the
> coherent dma mask from the current 64b to 31b. This will
> ensure that upper bits of the status block DMA address are
> always at most 0x7fff, thus avoiding the improper overflow
> check described above. This work around is intended for only
> status block and ring memories and has no effect on TX and
> RX buffers as they do not require coherent memory.
> 
> Fixes: 72f2afb8a685 ("[TG3]: Add DMA address workaround")
> Reported-by: Salam Noureddine <noureddine@...sta.com>
> Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@...adcom.com>
> Reviewed-by: Somnath Kotur <somnath.kotur@...adcom.com>
> Signed-off-by: Pavan Chebbi <pavan.chebbi@...adcom.com>
> ---
>  drivers/net/ethernet/broadcom/tg3.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
> index 378815917741..d178138981a9 100644
> --- a/drivers/net/ethernet/broadcom/tg3.c
> +++ b/drivers/net/ethernet/broadcom/tg3.c
> @@ -17801,6 +17801,9 @@ static int tg3_init_one(struct pci_dev *pdev,
>  	} else
>  		persist_dma_mask = dma_mask = DMA_BIT_MASK(64);
>  
> +	if (tg3_asic_rev(tp) == ASIC_REV_57766)
> +		persist_dma_mask = DMA_BIT_MASK(31);
> +
>  	/* Configure DMA attributes. */
>  	if (dma_mask > DMA_BIT_MASK(32)) {
>  		err = dma_set_mask(&pdev->dev, dma_mask);
> -- 
> 2.39.1
> 
> 

Reviewed-by: Michal Kubiak <michal.kubiak@...el.com>