linux-kernel - Re: [PATCH 1/3] Blackfin ethernet driver: on chip ethernet MAC controller driver

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Date:	Sun, 15 Jul 2007 09:04:21 -0400
From:	Dan Williams <dcbw@...hat.com>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Michael Buesch <mb@...sch.de>, bryan.wu@...log.com,
	Jeff Garzik <jeff@...zik.org>,
	LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] Blackfin ethernet driver: on chip ethernet MAC
	controller driver

On Sat, 2007-07-14 at 16:38 -0400, Mike Frysinger wrote:
> On 7/14/07, Michael Buesch <mb@...sch.de> wrote:
> > On Saturday 14 July 2007 21:49:21 Mike Frysinger wrote:
> > > On 7/14/07, Michael Buesch <mb@...sch.de> wrote:
> > > > On Saturday 14 July 2007 20:49:53 Bryan Wu wrote:
> > > > > +static int __init bf537mac_probe(struct net_device *dev)
> > > > > +{
> > > > > +     struct bf537mac_local *lp = netdev_priv(dev);
> > > > > +     int retval;
> > > > > +
> > > > > +     /* Grab the MAC address in the MAC */
> > > > > +     *(u32 *) (&(dev->dev_addr[0])) = bfin_read_EMAC_ADDRLO();
> > > > > +     *(u16 *) (&(dev->dev_addr[4])) = (u16) bfin_read_EMAC_ADDRHI();
> > > >
> > > > Endianess broken.
> > > >
> > > > > +struct dma_config_reg {
> > > > > +     unsigned short b_DMA_EN:1;  /* Bit 0 : DMA Enable */
> > > > > +     unsigned short b_WNR:1;     /* Bit 1 : DMA Direction */
> > > > > +     unsigned short b_WDSIZE:2;  /* Bit 2 & 3 : DMA Tranfer Word size */
> > > > > +     unsigned short b_DMA2D:1;   /* Bit 4 : DMA Mode 2D or 1D */
> > > > > +     unsigned short b_RESTART:1; /* Bit 5 : Retain the FIFO */
> > > > > +     unsigned short b_DI_SEL:1;  /* Bit 6 : Data Interrupt Timing Select */
> > > > > +     unsigned short b_DI_EN:1;   /* Bit 7 : Data Interrupt Enable */
> > > > > +     unsigned short b_NDSIZE:4;  /* Bit 8 to 11 : Flex descriptor Size */
> > > > > +     unsigned short b_FLOW:3;    /* Bit 12 to 14 : FLOW */
> > > > > +};
> > > >
> > > > This is most likely not endianess safe.
> > >
> > > do we really need to care about this ?  this is a driver for a MAC
> > > which can only be found on Blackfin processors and Blackfin itself is
> > > only little endian.
> >
> > Well, this bitfield _might_ be OK (although I don't like bitfields
> > at all), but the above pointer casting stuff should really use
> > leXX_to_cpu. It's so easy to use and it is easier to read and
> > maintain the code afterwards.
> 
> i think that's arguable ... i dont see how:
> a = foo(b);
> is easier to read than:
> a = b;
> but it is easy to use ... i guess my point was more along the lines of
> wasting further time auditing a driver for endianness issues that will
> never actually be an issue.

Sometimes by doing this you catch bugs you didn't see before.  It's a
good thing to do generally.  Does sparse with endianness check show
errors?  You may want to fix those.

Dan

> -mike
> -
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