netdev - Re: [PATCH v2 2/2] net: macb: Allocate valid memory for TX and RX BD prefetch

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Date:   Sat, 07 Jul 2018 20:55:21 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     harini.katakam@...inx.com
Cc:     nicolas.ferre@...rochip.com, claudiu.beznea@...rochip.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        michal.simek@...inx.com, harinikatakamlinux@...il.com
Subject: Re: [PATCH v2 2/2] net: macb: Allocate valid memory for TX and RX
 BD prefetch

From: Harini Katakam <harini.katakam@...inx.com>
Date: Fri, 6 Jul 2018 12:18:58 +0530

> GEM version in ZynqMP and most versions greater than r1p07 supports
> TX and RX BD prefetch. The number of BDs that can be prefetched is a
> HW configurable parameter. For ZynqMP, this parameter is 4.
> 
> When GEM DMA is accessing the last BD in the ring, even before the
> BD is processed and the WRAP bit is noticed, it will have prefetched
> BDs outside the BD ring. These will not be processed but it is
> necessary to have accessible memory after the last BD. Especially
> in cases where SMMU is used, memory locations immediately after the
> last BD may not have translation tables triggering HRESP errors. Hence
> always allocate extra BDs to accommodate for prefetch.
> The value of tx/rx bd prefetch for any given SoC version is:
> 2 ^ (corresponding field in design config 10 register).
> (value of this field >= 1)
> 
> Added a capability flag so that older IP versions that do not have
> DCFG10 or this prefetch capability are not affected.
> 
> Signed-off-by: Harini Katakam <harini.katakam@...inx.com>
> Reviewed-by: Claudiu Beznea <claudiu.beznea@...rochip.com>

Applied.