linux-kernel - Re: [Intel-wired-lan] [PATCH] e1000e: Remove useless DMA-32 fallback configuration

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Date:   Fri, 28 Jan 2022 12:19:44 +0200
From:   "Neftin, Sasha" <sasha.neftin@...el.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <kernel-janitors@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>,
        Christoph Hellwig <hch@....de>,
        "Neftin, Sasha" <sasha.neftin@...el.com>,
        "Avivi, Amir" <amir.avivi@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH] e1000e: Remove useless DMA-32 fallback
 configuration

On 1/9/2022 20:23, Christophe JAILLET wrote:
> As stated in [1], dma_set_mask() with a 64-bit mask never fails if
> dev->dma_mask is non-NULL.
> So, if it fails, the 32 bits case will also fail for the same reason.
> 
> So, if dma_set_mask_and_coherent() succeeds, 'pci_using_dac' is known to be
> 1.
> 
> Simplify code and remove some dead code accordingly.
> 
> [1]: https://lkml.org/lkml/2021/6/7/398
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> ---
>   drivers/net/ethernet/intel/e1000e/netdev.c | 22 +++++++---------------
>   1 file changed, 7 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 635a95927e93..4f6ee5c44f75 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -7385,9 +7385,9 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>   	resource_size_t flash_start, flash_len;
>   	static int cards_found;
>   	u16 aspm_disable_flag = 0;
> -	int bars, i, err, pci_using_dac;
>   	u16 eeprom_data = 0;
>   	u16 eeprom_apme_mask = E1000_EEPROM_APME;
> +	int bars, i, err;
>   	s32 ret_val = 0;
>   
>   	if (ei->flags2 & FLAG2_DISABLE_ASPM_L0S)
> @@ -7401,17 +7401,11 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>   	if (err)
>   		return err;
>   
> -	pci_using_dac = 0;
>   	err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
> -	if (!err) {
> -		pci_using_dac = 1;
> -	} else {
> -		err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> -		if (err) {
> -			dev_err(&pdev->dev,
> -				"No usable DMA configuration, aborting\n");
> -			goto err_dma;
> -		}
> +	if (err) {
> +		dev_err(&pdev->dev,
> +			"No usable DMA configuration, aborting\n");
> +		goto err_dma;
>   	}
>   
>   	bars = pci_select_bars(pdev, IORESOURCE_MEM);
> @@ -7547,10 +7541,8 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>   
>   	netdev->priv_flags |= IFF_UNICAST_FLT;
>   
> -	if (pci_using_dac) {
> -		netdev->features |= NETIF_F_HIGHDMA;
> -		netdev->vlan_features |= NETIF_F_HIGHDMA;
> -	}
> +	netdev->features |= NETIF_F_HIGHDMA;
> +	netdev->vlan_features |= NETIF_F_HIGHDMA;
>   
>   	/* MTU range: 68 - max_hw_frame_size */
>   	netdev->min_mtu = ETH_MIN_MTU;
Thank you Christophe
Acked-by: Sasha Neftin <sasha.neftin@...el.com>