linux-kernel - Re: [PATCH net-next 1/5] net: mvpp2: use the same buffer pool for all ports

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Message-ID: <20180305134148.3bbba514@windsurf.home>
Date:   Mon, 5 Mar 2018 13:41:48 +0100
From:   Thomas Petazzoni <thomas.petazzoni@...tlin.com>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     davem@...emloft.net, Stefan Chulski <stefanc@...vell.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        maxime.chevallier@...tlin.com, gregory.clement@...tlin.com,
        miquel.raynal@...tlin.com, nadavh@...vell.com,
        ymarkman@...vell.com, mw@...ihalf.com
Subject: Re: [PATCH net-next 1/5] net: mvpp2: use the same buffer pool for
 all ports

Hello,

On Mon, 5 Mar 2018 11:48:13 +0100, Antoine Tenart wrote:

> > > +static void mvpp2_setup_bm_pool(void)
> > > +{
> > > +	/* Short pool */
> > > +	mvpp2_pools[MVPP2_BM_SHORT].buf_num  = MVPP2_BM_SHORT_BUF_NUM;
> > > +	mvpp2_pools[MVPP2_BM_SHORT].pkt_size = MVPP2_BM_SHORT_PKT_SIZE;
> > > +
> > > +	/* Long pool */
> > > +	mvpp2_pools[MVPP2_BM_LONG].buf_num  = MVPP2_BM_LONG_BUF_NUM;
> > > +	mvpp2_pools[MVPP2_BM_LONG].pkt_size = MVPP2_BM_LONG_PKT_SIZE;
> > > +}  
> > 
> >  ?  
> 
> I wanted to do this, but it's no possible as MVPP2_BM_SHORT_PKT_SIZE and
> MVPP2_BM_LONG_PKT_SIZE use a core definition which expands at some point
> to __max(...) which has to be called from within a function.

Hum, weird:

#define MVPP2_BM_LONG_PKT_SIZE	MVPP2_RX_MAX_PKT_SIZE(MVPP2_BM_LONG_FRAME_SIZE)
#define MVPP2_BM_LONG_FRAME_SIZE		2048

#define MVPP2_RX_MAX_PKT_SIZE(total_size) \
        ((total_size) - NET_SKB_PAD - MVPP2_SKB_SHINFO_SIZE)

#define MVPP2_SKB_SHINFO_SIZE \
        SKB_DATA_ALIGN(sizeof(struct skb_shared_info))

#define SKB_DATA_ALIGN(X)        ALIGN(X, SMP_CACHE_BYTES)

I don't really see a __max(...) call.

And if this value really expands depending on other values, then it
isn't really a constant, and should be considered as a constant, no?

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com