[U-Boot] [PATCH] fastboot: Fix OUT transaction length alignment

[Tom Rini]

On Wed, Apr 13, 2016 at 03:01:02PM +0300, Semen Protsenko wrote:

> From: Sam Protsenko <semen.protsenko at linaro.org>
> 
> Some UDC controllers may require buffer size to be aligned to
> wMaxPacketSize. It's indicated by gadget->quirk_ep_out_aligned_size
> field being set to "true" (in UDC driver code). In that case
> rx_bytes_expected must be aligned to wMaxPacket size, otherwise stuck on
> transaction will happen. For example, it's required by DWC3 controller
> data manual:
> 
>     section 8.2.3.3 Buffer Size Rules and Zero-Length Packets:
> 
>     For OUT endpoints, the following rules apply:
>     - The BUFSIZ field must be ≥ 1 byte.
>     - The total size of a Buffer Descriptor must be a multiple of
>       MaxPacketSize
>     - A received zero-length packet still requires a MaxPacketSize buffer.
>       Therefore, if the expected amount of data to be received is a multiple
>       of MaxPacketSize, software should add MaxPacketSize bytes to the buffer
>       to sink a possible zero-length packet at the end of the transfer.
> 
> But other UDC controllers don't need such alignment, so mentioned field
> is set to "false". If buffer size is aligned to wMaxPacketSize, those
> controllers may stuck on transaction. The example is DWC2.
> 
> This patch checks gadget->quirk_ep_out_aligned_size field and aligns
> rx_bytes_expected to wMaxPacketSize only when it's needed.
[snip]
> @@ -435,12 +438,18 @@ static unsigned int rx_bytes_expected(unsigned int maxpacket)
>  		return 0;
>  	if (rx_remain > EP_BUFFER_SIZE)
>  		return EP_BUFFER_SIZE;
> +
> +	if (!quirk_ep_out_aligned_size)
> +		goto out;
> +
>  	if (rx_remain < maxpacket) {
>  		rx_remain = maxpacket;
>  	} else if (rx_remain % maxpacket != 0) {
>  		rem = rx_remain % maxpacket;
>  		rx_remain = rx_remain + (maxpacket - rem);
>  	}
> +
> +out:
>  	return rx_remain;

Can we do:
/* Only continue on conntrollers that require additional padding */
if (!quirk_ep_out_aligned_size)
	return rx_remain;

Or similar comment, so it's clear in the code why we're doing this and
no need for a new goto here.  Thanks!

-- 
Tom
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