linux-kernel - Re: [PATCH v3 2/3] i2c: add support for Diolan DLN-2 USB-I2C adapter

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Date:	Mon, 8 Sep 2014 18:30:58 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	Johan Hovold <johan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>, wsa@...-dreams.de,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Daniel Baluta <daniel.baluta@...el.com>,
	Laurentiu Palcu <laurentiu.palcu@...el.com>,
	linux-usb@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH v3 2/3] i2c: add support for Diolan DLN-2 USB-I2C adapter

On Mon, Sep 08, 2014 at 06:57:29PM +0300, Octavian Purdila wrote:
> On Mon, Sep 8, 2014 at 5:44 PM, Johan Hovold <johan@...nel.org> wrote:
> 
> <snip>
> 
> Hi Johan,
> 
> Again, thanks for the detailed review, I am addressing your review
> comments as we speak. Some questions below.
> 
> <snip>
> 
> > > +     int ret, len;
> > > +     struct tx_data {
> > > +             u8 port;
> > > +             u8 addr;
> > > +             u8 mem_addr_len;
> > > +             __le32 mem_addr;
> > > +             __le16 buf_len;
> > > +             u8 buf[DLN2_I2C_MAX_XFER_SIZE];
> > > +     } __packed tx;
> >
> > Allocate these buffers dynamically (possibly at probe).
> >
> 
> I double checked this, and DLN2_I2C_MAX_XFER_SIZE should actually be <
> 64 as the USB endpoint configuration max packet size is 64. In this
> case, can we keep it on the stack?

It's better to lift that restriction and allocate it dynamically. Using
larger buffers (> EP size) is also more efficient.

> <snip>
> 
> > > +     int ret, buf_len, rx_len = sizeof(rx);
> >
> > Again, one declaration per line.
> 
> AFAICS there are many places where declaration on the same line
> (initialization included) are used. When did this became a coding
> style issue?

It's ugly, hurts readability, and can also obfuscate the fact that your
function really needs to be refactored.

And it's in the CodingStyle:

	"To this end, use just one data declaration per line (no commas
	for multiple data declarations)."

Johan
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