Hi Andrew,
From: Andrew Lunn <and...@lunn.ch>
Sent: Friday, August 19, 2016 7:39 PM
To: Claudiu Manoil
Cc: Zefir Kurtisi; netdev@vger.kernel.org; claudiu.man...@freescale.com
Subject: Re: [PATCH] gianfar: prevent fragmentation in DSA environments
> >> -#define GFAR_RXB_SIZE 1536
> >> +/* prevent fragmenation by HW in DSA environments */
> >> +#define GFAR_RXB_SIZE (1536 + RXBUF_ALIGNMENT)
> >
> >Hi Zefir
> >
> >Using RXBUF_ALIGNMENT suggests this has something to do with
> >alignment, not extra headers.
> >
> >How about
> >
> >/* Prevent fragmenation by HW when using extra headers like DSA */
> >#define GFAR_RXB_SIZE (1536 + 8)
> >
>
> MRBL (Maximum receive buffer length) must be multiple of 64.
> Please consult de hardware documentation at least before prosing
> changes to the driver.
Hi Claudiu
Thanks for pointing this out. This makes RXBUF_ALIGNMENT even worse
for understabability, since you say multiples of 64 is important, not
alignment.
How about
/* Prevent fragmentation by HW when using extra headers like DSA,
while respecting the multiple of 64 requirement. */
#define GFAR_RXB_SIZE roundup(1536 + 8, 64)
[Claudiu]
Nice improvement.
But what's so special about 8? I thought only 4 bytes were missing :)
At least 1536 is the default size of the MRBLR register, as specified
in the h/w ref manual. Is there some recommended standard size
to accommodate most (if not all) headers, to refer to?
