From: Ben Dooks
> Sent: 02 October 2018 10:27
>
> The tegra driver requires alignment of the buffer, so try and
> make this better by pushing the buffer start back to an word
> aligned address. At the worst this makes memcpy() easier as
> it is word aligned, at best it makes sure the usb can directly
> map the buffer.
>
> Signed-off-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
> [todo - make this configurable]
> ---
> drivers/net/usb/Kconfig | 12 ++++++++++++
> drivers/net/usb/smsc95xx.c | 22 ++++++++++++++++++++--
> 2 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/usb/Kconfig b/drivers/net/usb/Kconfig
...
> +static bool align_tx = IS_ENABLED(CONFIG_USB_NET_SMSC95XX_TXALIGN);
> +module_param(align_tx, bool, 0644);
> +MODULE_PARM_DESC(align_tx, "Align TX buffers to word boundaries");
DM doesn't like module parameters.
> static bool turbo_mode = IS_ENABLED(CONFIG_USB_NET_SMSC95XX_TURBO);
> module_param(turbo_mode, bool, 0644);
> MODULE_PARM_DESC(turbo_mode, "Enable multiple frames per Rx transaction");
> @@ -2005,10 +2009,18 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
> bool csum = skb->ip_summed == CHECKSUM_PARTIAL;
> int overhead = csum ? SMSC95XX_TX_OVERHEAD_CSUM : SMSC95XX_TX_OVERHEAD;
> u32 tx_cmd_a, tx_cmd_b;
> + u32 data_len;
> + uintptr_t align = 0;
>
> /* We do not advertise SG, so skbs should be already linearized */
> BUG_ON(skb_shinfo(skb)->nr_frags);
>
> + if (IS_ENABLED(CONFIG_USB_NET_SMSC95XX_TXALIGN) && align_tx) {
> + align = (uintptr_t)skb->data & 3;
> + if (align)
> + overhead += 4 - align;
Better to calculate the pad size once:
align = (-(long)skb->data) & 3;
should do it - and you can unconditionally add it in.
> + }
> +
> /* Make writable and expand header space by overhead if required */
> if (skb_cow_head(skb, overhead)) {
> /* Must deallocate here as returning NULL to indicate error
> @@ -2037,16 +2049,22 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
> }
> }
>
> + data_len = skb->len;
> + if (align)
> + skb_push(skb, 4 - align);
> +
> skb_push(skb, 4);
You don't want to call skb_push() twice.
IIRC really horrid things happen if the data has to be copied.
(Actually what happens to the alignment in that case??)
And there is another skb_push() below....
> - tx_cmd_b = (u32)(skb->len - 4);
> + tx_cmd_b = (u32)(data_len);
You don't need the cast here at all (if it was ever needed).
Actually you don't need the new 'data_len' variable.
Just set tx_cmd_b earlier.
...
David
-
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