linux-kernel - Re: [spi-devel-general] [PATCH v4] powerpc/5200: Add mpc5200-spi (non-PSC) device driver

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Message-ID: <20090618142610.GC10629@pengutronix.de>
Date:	Thu, 18 Jun 2009 16:26:10 +0200
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linuxppc-dev@...abs.org,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, jonsmirl@...il.com
Subject: Re: [spi-devel-general] [PATCH v4] powerpc/5200: Add mpc5200-spi
	(non-PSC) device driver

Hi Grant,

> The double spaces at the end of sentences are intentional.  It is
> perhaps a bit quaint and old fashioned, but it is my writing style.

Ah, okay.

> >> +
> >> +     /* Statistics */
> >> +     int msg_count;
> >> +     int wcol_count;
> >> +     int wcol_ticks;
> >> +     u32 wcol_tx_timestamp;
> >> +     int modf_count;
> >> +     int byte_count;
> >
> > Hmm, there isn't even a debug-printout for those. Putting #ifdef DEBUG around
> > them will be ugly. Well, I can't make up if this is just overhead or useful
> > debugging aid, so no real objection :)
> 
> There used to be a sysfs interface for dumping these, but it was an
> ugly misuse.  I'd like to leave these in.  I still have the sysfs bits
> in a private patch and I'm going to rework them for debugfs.

Okay. Maybe a comment stating the future use will be nice.

> 
> > But I wonder more about the usage of the SS pin and if this chipsel is needed
> > at all (sadly I cannot test as I don't have any board with SPI connected to
> > that device). You define the SS-pin as output, but do not set the SSOE-bit.
> > More, you use the MODF-feature, so the SS-pin should be defined as input?
> > According to Table 17.3 in the PM, you have that pin defined as generic purpose
> > output.
> 
> That's right.  The SS handling by the SPI device is completely
> useless, so this driver uses it as a GPIO and asserts it manually.

That definately needs a comment :D (perhaps with some more details if you know them).

> The MODF irq is probably irrelevant, but I'd like to leave it in for
> completeness.

But it won't work if the pin is set to output, no? Are you sure there are no
side-effects?


> >> +     /* initialize the device */
> >> +     out_8(regs+SPI_CTRL1, SPI_CTRL1_SPIE | SPI_CTRL1_SPE | SPI_CTRL1_MSTR);
> >
> > spaces around operator.
> 
> Intentional to keep from spilling past column 80; but I'll move the
> missing spaces to around the | operators.  I think it is easier to
> read that way.

Ah, I remember, we had this topic a while ago :D

Regards,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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