netdev - Re: [PATCH] r8169: set coherent DMA mask as well as streaming DMA mask

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Date:   Fri, 14 Oct 2016 14:32:24 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     David Miller <davem@...emloft.net>
Cc:     Francois Romieu <romieu@...zoreil.com>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] r8169: set coherent DMA mask as well as streaming DMA mask

On 14 October 2016 at 14:31, David Miller <davem@...emloft.net> wrote:
> From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Date: Fri, 14 Oct 2016 12:39:30 +0100
>
>> PCI devices that are 64-bit DMA capable should set the coherent
>> DMA mask as well as the streaming DMA mask. On some architectures,
>> these are managed separately, and so the coherent DMA mask will be
>> left at its default value of 32 if it is not set explicitly. This
>> results in errors such as
>>
>>      r8169 Gigabit Ethernet driver 2.3LK-NAPI loaded
>>      hwdev DMA mask = 0x00000000ffffffff, dev_addr = 0x00000080fbfff000
>>      swiotlb: coherent allocation failed for device 0000:02:00.0 size=4096
>>      CPU: 0 PID: 1062 Comm: systemd-udevd Not tainted 4.8.0+ #35
>>      Hardware name: AMD Seattle/Seattle, BIOS 10:53:24 Oct 13 2016
>>
>> on systems without memory that is 32-bit addressable by PCI devices.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>  ...
>> @@ -8281,6 +8282,8 @@ static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>>               dev->features |= NETIF_F_HIGHDMA;
>>       } else {
>>               rc = pci_set_dma_mask(pdev, DMA_BIT_MASK(32));
>> +             if (!rc)
>> +                     rc = pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(32));
>
> As you state 32-bit is the default, therefore this part of your patch is unnecessary.

Perhaps, but the original code did not assume that either. Should I
remove the other call in a subsequent patch as well?