linux-kernel - Re: [PATCH] BugFix in XHCI controller driver for scatter gather DMA

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Message-ID: <5677EFA1.8050309@cogentembedded.com>
Date:	Mon, 21 Dec 2015 15:25:05 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Vikas Bansal <vikas.bansal@...sung.com>, mathias.nyman@...el.com,
	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	sumit.batra@...sung.com
Subject: Re: [PATCH] BugFix in XHCI controller driver for scatter gather DMA

Hello.

On 12/21/2015 3:15 PM, Vikas Bansal wrote:

> From: Sumit Batra <sumit.batra@...sung.com>
>
> Pre-Condition
> URB with Scatter Gather list is queued to bulk OUT endpoint.
> Every buffer in scatter gather list is not a multiple of maximum packet size for that endpoint(short packet).
> CHAIN bit is set for all TRBs in a TD so that the DMA happens to all of them at once.
>
> Issue
> DMA operation copies all the CHAINED TRBs at contiguous device memory.
> But since the original packet was a short packet, so the actual data is re-aligned after this DMA operation.
> At device end this re-aligned data causes data integrity issue with applications like ICMP ping.
>
> Solution
> Don't set the CHAINED bit for these TRBs, if their buffers are not a multiple of maximum packet size.
> This will reduce the benefit in throughput as required from a scatter gather implementation, but this reduces the CPU utilization.
> And solves the data integrity issue on Device End
>
>
> Signed-off-by: Sumit Batra <sumit.batra@...sung.com>
> Signed-off-by: Vikas Bansal <vikas.bansal@...sung.com>
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index 7d34cbf..862d7cd 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -3110,7 +3110,8 @@ static int queue_bulk_sg_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
>   		 * TRB to indicate it's the last TRB in the chain.
>   		 */
>   		if (num_trbs > 1) {
> -			field |= TRB_CHAIN;
> +			if(this_sg_len % usb_endpoint_maxp(&urb->ep->desc) == 0)

    Space needed after *if*. Please run your patches thru scripts/checkpatch.pl.

[...]

MBR, Sergei

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