netdev - RE: [PATCH v3 1/6] net: fec: Factorize the .xmit transmit function

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Date:	Thu, 5 Jun 2014 09:34:44 +0000
From:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
To:	David Laight <David.Laight@...LAB.COM>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"Fabio.Estevam@...escale.com" <Fabio.Estevam@...escale.com>,
	"ezequiel.garcia@...e-electrons.com" 
	<ezequiel.garcia@...e-electrons.com>,
	"bhutchings@...arflare.com" <bhutchings@...arflare.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>,
	"Frank.Li@...escale.com" <Frank.Li@...escale.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: RE: [PATCH v3 1/6] net: fec: Factorize the .xmit transmit function

From: David Laight <David.Laight@...LAB.COM> Data: Thursday, June 05, 2014 5:07 PM
> To: Duan Fugang-B38611; davem@...emloft.net
> Cc: netdev@...r.kernel.org; shawn.guo@...aro.org; Estevam Fabio-R49496;
> ezequiel.garcia@...e-electrons.com; bhutchings@...arflare.com;
> stephen@...workplumber.org; Li Frank-B20596; eric.dumazet@...il.com
> Subject: RE: [PATCH v3 1/6] net: fec: Factorize the .xmit transmit function
> 
> From: Fugang Duan
> > Make the code more readable and easy to support other features like
> > SG, TSO, moving the common transmit function to one api.
> >
> > And the patch also factorize the getting BD index to it own function.
> >
> > Signed-off-by: Fugang Duan <B38611@...escale.com>
> > ---
> >  drivers/net/ethernet/freescale/fec_main.c |   87 ++++++++++++++++++-----
> ------
> >  1 files changed, 54 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/fec_main.c
> > b/drivers/net/ethernet/freescale/fec_main.c
> > index 802be17..32c2276 100644
> > --- a/drivers/net/ethernet/freescale/fec_main.c
> > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > @@ -287,6 +287,25 @@ struct bufdesc *fec_enet_get_prevdesc(struct bufdesc
> *bdp, struct fec_enet_priva
> >  		return (new_bd < base) ? (new_bd + ring_size) : new_bd;  }
> >
> > +static inline
> > +int fec_enet_get_bd_index(struct bufdesc *bdp, struct
> > +fec_enet_private *fep) {
> > +	struct bufdesc *base;
> > +	int index;
> > +
> > +	if (bdp >= fep->tx_bd_base)
> > +		base = fep->tx_bd_base;
> > +	else
> > +		base = fep->rx_bd_base;
> 
> You really don't want the above conditional.
> It is known from the call site - but the compiler can't determine that and
> remove the test.
Can you give me more training for this ?  Sorry, I don't understand the means. 

> You may not want to rely on the tx and rx descriptors being allocated as a
> single entity - particularly now that they (probably) consume more than a
> single page.
> 
BDs consumes more than single page, but it use " dma_alloc_coherent()" to allocate continuous memory,
I don't know why it is cannot do it like this.

> > +
> > +	if (fep->bufdesc_ex)
> > +		index = (struct bufdesc_ex *)bdp - (struct bufdesc_ex *)base;
> > +	else
> > +		index = bdp - base;
> 
> Save the sizeof the descriptor structure as (say) fep->bufdesc_size
> (Possibly replacing bufdesc_ex) and then just calculate:
> 	index = ((const char *)bdp - (const char *)base)/fep->bufdesc_size;
> 
> 	David
> 
You means:
if (fep->bufdesc_ex)
	bufdesc_size = sizeof(struct bufdesc_ex);
else
	bufdesc_size = sizeof(struct bufdesc);
index = ((const char *)bdp - (const char *)base)/bufdesc_size;


Thanks,
Andy
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