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Subject: Re: [PATCH] mt76: usb: use EP max packet aligned buffer sizes for rx
To:     Stanislaw Gruszka <sgruszka@redhat.com>,
        linux-wireless@vger.kernel.org
Cc:     Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
References: <20190430074219.8495-1-sgruszka@redhat.com>
From:   Felix Fietkau <nbd@nbd.name>
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Date:   Tue, 30 Apr 2019 09:59:32 +0200
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On 2019-04-30 09:42, Stanislaw Gruszka wrote:
> If buffer size is not usb_endpoint_maxp (512 or 1024 bytes) multiple,
> usb host driver has to use bounce buffer and copy data. For RX we can
> avoid that since we alreay allocate q->buf_size (2kB) buffers and
> mt76usb hardware will not fill more data as rx packet size is limited
> by network protocol. However add error message if this assumption
> somehow will be not true.
> 
> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
> ---
>  drivers/net/wireless/mediatek/mt76/usb.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> index c299c6591072..025e072cff28 100644
> --- a/drivers/net/wireless/mediatek/mt76/usb.c
> +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> @@ -447,8 +446,10 @@ mt76u_process_rx_entry(struct mt76_dev *dev, struct urb *urb)
>  		return 0;
>  
>  	data_len = min_t(int, len, data_len - MT_DMA_HDR_LEN);
> -	if (MT_DMA_HDR_LEN + data_len > SKB_WITH_OVERHEAD(q->buf_size))
> +	if (MT_DMA_HDR_LEN + data_len > SKB_WITH_OVERHEAD(q->buf_size)) {
> +		dev_err(dev->dev, "rx data too big %d\n", data_len);
Please use WARN_ON_ONCE here, or at least dev_err_ratelimited if you
think it's necessary to print data_len.

- Felix