Re: [PATCH 1/1] can: gs_usb: remove dma allocations

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 13.09.2022 16:41:10, Rhett Aultman wrote:
> From: Vasanth Sadhasivan <vasanth.sadhasivan@samsara.com>
> 
> DMA allocated buffers are a precious resource. If there is no need for DMA
> allocations, then it might be worth to use non-dma allocated buffers.
> After testing the gs_usb driver with and without DMA allocation, there
> does not seem to be a significant change in latency or cpu utilization
> either way. Therefore, DMA allocation is not necessary and removed.
> 
> Co-developed-by: Rhett Aultman <rhett.aultman@samsara.com>
> Signed-off-by: Rhett Aultman <rhett.aultman@samsara.com>
> Signed-off-by: Vasanth Sadhasivan <vasanth.sadhasivan@samsara.com>
> ---
>  drivers/net/can/usb/gs_usb.c | 38 ++++++++++--------------------------
>  1 file changed, 10 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
> index baf749c8cda3..1bfc775c62c5 100644
> --- a/drivers/net/can/usb/gs_usb.c
> +++ b/drivers/net/can/usb/gs_usb.c
> @@ -269,7 +269,6 @@ struct gs_can {
>  	struct usb_anchor tx_submitted;
>  	atomic_t active_tx_urbs;
>  	void *rxbuf[GS_MAX_RX_URBS];
> -	dma_addr_t rxbuf_dma[GS_MAX_RX_URBS];
>  };
>  
>  /* usb interface struct */
> @@ -587,9 +586,7 @@ static void gs_usb_xmit_callback(struct urb *urb)
>  
>  	if (urb->status)
>  		netdev_info(netdev, "usb xmit fail %u\n", txc->echo_id);
> -
> -	usb_free_coherent(urb->dev, urb->transfer_buffer_length,
> -			  urb->transfer_buffer, urb->transfer_dma);
> +	devm_kfree(&urb->dev->dev, urb->transfer_buffer);

Consider using the URB_FREE_BUFFER flag:

| https://elixir.bootlin.com/linux/v5.19/source/include/linux/usb.h#L1330

and standard kmalloc() (i.e. not devm_kmalloc()). The USB stack will
take care of kfree()ing the buffer associated with each URB.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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