Re: [PATCH 1/2] staging: iio replaced kmalloc with local variables.

[anish kumar]

Jonathan Cameron wrote:
> On 06/07/11 05:56, anish singh wrote:
> > On Tue, Jun 7, 2011 at 4:11 AM, Greg KH <gregkh@xxxxxxx
> > <mailto:gregkh@xxxxxxx>> wrote:
> >
> >     On Mon, Jun 06, 2011 at 03:28:29PM -0700, Joe Perches wrote:
> >     > On Mon, 2011-06-06 at 15:21 -0700, Greg KH wrote:
> >     > > On Mon, Jun 06, 2011 at 03:10:57PM -0700, Joe Perches wrote:
> >     > > > On Mon, 2011-06-06 at 14:55 -0700, Greg KH wrote:
> >     > > > > On Tue, Jun 07, 2011 at 12:37:37AM +0530, anish wrote:
> >     > > > > > From: anish kumar <anish198519851985@xxxxxxxxx
> >     <mailto:anish198519851985@xxxxxxxxx>> > > > > > Replace kmalloc with
> >     local variables as it was un-necessary and > > > > > also removed the
> >     redudant code after this change. > > > > SPI data, like USB data, has to
> >     come from kmalloced data, not from the > > > > stack, or bad things can,
> >     and will, happen. > > > Perhaps just add a comment like:
> >     > > > +       u8 *tx = kmalloc(2, GFP_KERNEL);  /* can't be on stack */
> >     > > You really want to do to that for _EVERY_ SPI and USB driver?  I
> >     don't > > think so.
> >     >
> >     > Nope, only the ones that look especially odd because
> >     >       kmalloc(sizeof(struct foo), ...)
> >     > or
> >     >       kmalloc(sizeof("type), ...)
> >     > is not used.
> >     >
> >     > It might be better to just declare a 2 byte struct.
> >
> >     No, this is a very common thing for all USB and SPI drivers.  It's so
> >     obvious that once I saw the Subject: line, I knew this patch was going
> >     to be wrong.
> >
> >     This is something that the USB and SPI developers know all about, it's
> >     the way things work, and this driver works, so why are people trying to
> >     "clean" it up in ways that will break it, or cause extra work with
> >     structures where they are not needed at all?
> >
> > Sorry for noise as i didn't the SPI requirements,thought it is similar to
> > I2C and
> > in cleaning up below part i wrongly cleaned SPI part also.Below was also part
> > of patch.
> Not to worry, you are far from the first person to fall into this issue!
> Also, you have highlighted a weird corner in that driver, that could do with
> tidying up (just not quite the fix you had in mind!).
> > static int max1363_write_basic_config(struct i2c_client *client,
> >                                      unsigned char d2)
> >  {
> >        int ret;
> > -       u8 *tx_buf = kmalloc(2, GFP_KERNEL);
> > +       u8 tx_buf[2];
> >        if (!tx_buf)
> >                return -ENOMEM;
> > @@ -215,7 +215,6 @@ static int max1363_write_basic_config(struct i2c_client
> >        *client, tx_buf[1] = d2;
> >        ret = i2c_master_send(client, tx_buf, 2);
> > -       kfree(tx_buf);
> >        return (ret > 0) ? 0 : ret;
> >  }
> > I think above patch is ok as it is I2C and I2C doesn't have that requirement.
> Yes.  I2C bus drivers that do dma do the copy into dma safe memory internally.
> Makes for more bouncing around of data, but i2c is slow anyway so it doesn't
> matter. Also, based on a quick look this morning, the dma buffers tend to
> require various headers to be in place etc which isn't typically the case for
> spi (a much more 'raw' bus).
I couldn't understand this comment.Specifically "various headers"?
Will appreciate it if you kindly explain.
> Can you cc linux-iio@xxxxxxxxxxxxxxx on that patch when you send it out
> please.
Sure.Sorry for not sending it there.
> Jonathan 

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