linux-kernel - Re: [RFC PATCH 02/06] input/rmi4: Core files

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Date:	Tue, 23 Oct 2012 17:11:41 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Christopher Heiny <cheiny@...aptics.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Jean Delvare <khali@...ux-fr.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Input <linux-input@...r.kernel.org>,
	Allie Xiong <axiong@...aptics.com>,
	Vivian Ly <vly@...aptics.com>,
	Daniel Rosenberg <daniel.rosenberg@...aptics.com>,
	Joerie de Gram <j.de.gram@...il.com>,
	Wolfram Sang <w.sang@...gutronix.de>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Naveen Kumar Gaddipati <naveen.gaddipati@...ricsson.com>,
	Alexandra Chin <alexandra.chin@...synaptics.com>
Subject: Re: [RFC PATCH 02/06] input/rmi4: Core files

On Tuesday, October 23, 2012 04:46:28 PM Christopher Heiny wrote:
> On 10/11/2012 01:13 AM, Dmitry Torokhov wrote:
> > On Thu, Oct 11, 2012 at 04:15:56AM +0000, Christopher Heiny wrote:
> >> On Thursday, October 11, 2012 02:21:53 AM you wrote:
> >>> On Sat, Oct 6, 2012 at 6:09 AM, Christopher Heiny <cheiny@...aptics.com> 
wrote:
> >>>> +
> >>>> +/** This is here because all those casts made for some ugly code.
> >>>> + */
> >>>> +static void u8_and(u8 *dest, u8 *target1, u8 *target2, int nbits)
> >>>> +{
> >>>> +       bitmap_and((long unsigned int *) dest,
> >>>> +                  (long unsigned int *) target1,
> >>>> +                  (long unsigned int *) target2,
> >>>> +                  nbits);
> >>>> +}
> >>> 
> >>> Hm, getting rid of unreadable casts is a valid case.
> >>> 
> >>> I'll be OK with this but maybe the real solution is to introduce such
> >>> helpers into <linux/bitmap.h>?
> >> 
> >> Hmmm.  We'll give that some thought.  Thought I'd like to get the RMI4
> >> driver nailed down, just to keep the area of change small.  Once we've
> >> got all the kinks worked out here, we'll look at bitmap.h helpers.
> > 
> > The question is why you are using u8 for bitmaps instead of doing
> > DECALRE_BITMAP() and using it instead? Then you would not need silly
> > wrappers around existing APIs.
> 
> OK, we'll look into that.  My big concern is whether the bit-order in
> bitmask.h will be the same as the bit order in the RMI4 sensor
> registers.  If that works out OK, we'll switch.

I think if you properly convert data to/from cpu-endianness it will clear 
matters a lot.


> 
> >>> (...)
> >>> 
> >>>> +static int process_interrupt_requests(struct rmi_device *rmi_dev)
> >>>> +{
> >>>> +       struct rmi_driver_data *data = dev_get_drvdata(&rmi_dev->dev);
> >>>> +       struct device *dev = &rmi_dev->dev;
> >>>> +       struct rmi_function_container *entry;
> >>>> +       u8 irq_status[data->num_of_irq_regs];
> >>> 
> >>> Looking at this...
> >>> 
> >>> What does the data->num_of_irq_regs actually contain?
> >>> 
> >>> I just fear that it is something constant like always 2 or always 4,
> >>> so there is actually, in reality, a 16 or 32 bit register hiding in
> >>> there.
> >>> 
> >>> In that case what you should do is to represent it as a u16 or u32 here,
> >>> just or the bits into a status word, and then walk over that status
> >>> word with something like ffs(bitword); ...
> >> 
> >> Nope, it's not constant.  In theory, and RMI4 based sensor can have up
> >> to 128 functions (in practice, it's far fewer), and each function can
> >> have as many as 7 interrupts.  So the number of IRQ registers can vary
> >> from RMI4 sensor to RMI4 sensor, and needs to be computed during the
> >> scan of the product descriptor table.
> > 
> > Is it a good idea to have it on stack then? Should it be part of
> > rmi_device instead?
> 
> It's not coming off the stack.  We're allocating it via devm_kzalloc()
> in rmi_driver_probe().

No, look at the part of the code that was quoted. "u8 irq_status[data-
>num_of_irq_regs];" is on stack.

Thanks.

-- 
Dmitry
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