linux-kernel - Re: [PATCH v2 2/2] rtw88: pci: Use DMA sync instead of remapping in RX ISR

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Date:   Tue, 9 Jul 2019 09:15:50 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jian-Hong Pan <jian-hong@...lessm.com>
Cc:     Yan-Hsuan Chuang <yhchuang@...ltek.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Larry Finger <Larry.Finger@...inger.net>,
        David Laight <David.Laight@...lab.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...lessm.com,
        Daniel Drake <drake@...lessm.com>
Subject: Re: [PATCH v2 2/2] rtw88: pci: Use DMA sync instead of remapping in
 RX ISR

On Tue, Jul 09, 2019 at 06:21:01PM +0800, Jian-Hong Pan wrote:
> Since each skb in RX ring is reused instead of new allocation, we can
> treat the DMA in a more efficient way by DMA synchronization.
> 
> Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> ---
>  drivers/net/wireless/realtek/rtw88/pci.c | 35 ++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
> index e9fe3ad896c8..28ca76f71dfe 100644
> --- a/drivers/net/wireless/realtek/rtw88/pci.c
> +++ b/drivers/net/wireless/realtek/rtw88/pci.c
> @@ -206,6 +206,35 @@ static int rtw_pci_reset_rx_desc(struct rtw_dev *rtwdev, struct sk_buff *skb,
>  	return 0;
>  }
>  
> +static int rtw_pci_sync_rx_desc_cpu(struct rtw_dev *rtwdev, dma_addr_t dma)
> +{
> +	struct device *dev = rtwdev->dev;
> +	int buf_sz = RTK_PCI_RX_BUF_SIZE;
> +
> +	dma_sync_single_for_cpu(dev, dma, buf_sz, PCI_DMA_FROMDEVICE);
> +
> +	return 0;
> +}

No need to return a value from this helper. In fact I'm not even sure
you need the helper at all.  Also please use the DMA_FROM_DEVICE
constant instead of the deprecated PCI variant.

> +static int rtw_pci_sync_rx_desc_device(struct rtw_dev *rtwdev, dma_addr_t dma,
> +				       struct rtw_pci_rx_ring *rx_ring,
> +				       u32 idx, u32 desc_sz)
> +{
> +	struct device *dev = rtwdev->dev;
> +	struct rtw_pci_rx_buffer_desc *buf_desc;
> +	int buf_sz = RTK_PCI_RX_BUF_SIZE;
> +
> +	dma_sync_single_for_device(dev, dma, buf_sz, PCI_DMA_FROMDEVICE);
> +
> +	buf_desc = (struct rtw_pci_rx_buffer_desc *)(rx_ring->r.head +
> +						     idx * desc_sz);
> +	memset(buf_desc, 0, sizeof(*buf_desc));
> +	buf_desc->buf_size = cpu_to_le16(RTK_PCI_RX_BUF_SIZE);
> +	buf_desc->dma = cpu_to_le32(dma);
> +
> +	return 0;
> +}

Same comment on the PCI constant and the return value here.