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SubjectRe: [PATCH] net: mscc: fix in frame extraction
On 17/02/2020 09:31:33+0100, Horatiu Vultur wrote:
> Each extracted frame on Ocelot has an IFH. The frame and IFH are extracted
> by reading chuncks of 4 bytes from a register.
>
> In case the IFH and frames were read corretly it would try to read the next
> frame. In case there are no more frames in the queue, it checks if there
> were any previous errors and in that case clear the queue. But this check
> will always succeed also when there are no errors. Because when extracting
> the IFH the error is checked against 4(number of bytes read) and then the
> error is set only if the extraction of the frame failed. So in a happy case
> where there are no errors the err variable is still 4. So it could be
> a case where after the check that there are no more frames in the queue, a
> frame will arrive in the queue but because the error is not reseted, it
> would try to flush the queue. So the frame will be lost.
>
> The fix consist in resetting the error after reading the IFH.
>
> Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

> ---
> drivers/net/ethernet/mscc/ocelot_board.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/net/ethernet/mscc/ocelot_board.c b/drivers/net/ethernet/mscc/ocelot_board.c
> index b38820849faa..1135a18019c7 100644
> --- a/drivers/net/ethernet/mscc/ocelot_board.c
> +++ b/drivers/net/ethernet/mscc/ocelot_board.c
> @@ -114,6 +114,14 @@ static irqreturn_t ocelot_xtr_irq_handler(int irq, void *arg)
> if (err != 4)
> break;
>
> + /* At this point the IFH was read correctly, so it is safe to
> + * presume that there is no error. The err needs to be reset
> + * otherwise a frame could come in CPU queue between the while
> + * condition and the check for error later on. And in that case
> + * the new frame is just removed and not processed.
> + */
> + err = 0;
> +
> ocelot_parse_ifh(ifh, &info);
>
> ocelot_port = ocelot->ports[info.port];
> --
> 2.17.1
>

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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