linux-kernel - Re: [PATCH v2 01/13] mfd: pruss mfd driver.

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Date:	Tue, 22 Feb 2011 11:48:51 +0100
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Samuel Ortiz <sameo@...ux.intel.com>
CC:	Subhasish Ghosh <subhasish@...tralsolutions.com>,
	sachi@...tralsolutions.com,
	davinci-linux-open-source@...ux.davincidsp.com, nsekhar@...com,
	open list <linux-kernel@...r.kernel.org>, m-watkins@...com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 01/13] mfd: pruss mfd driver.

On 02/22/2011 11:31 AM, Samuel Ortiz wrote:
> Hi Subhasish,
> 
> On Tue, Feb 22, 2011 at 11:13:38AM +0530, Subhasish Ghosh wrote:
>> Thank you for your comments.
> No problem.
> 
>>>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>>>> index fd01836..6c437df 100644
>>>> --- a/drivers/mfd/Kconfig
>>>> +++ b/drivers/mfd/Kconfig
>>>> @@ -81,6 +81,16 @@ config MFD_DM355EVM_MSP
>>>>   boards.  MSP430 firmware manages resets and power sequencing,
>>>>   inputs from buttons and the IR remote, LEDs, an RTC, and more.
>>>>
>>>> +config MFD_DA8XX_PRUSS
>>>> + tristate "Texas Instruments DA8XX PRUSS support"
>>>> + depends on ARCH_DAVINCI && ARCH_DAVINCI_DA850
>>> Why are we depending on those ?
>>
>> SG -- The PRUSS core in only available within DA850 and DA830,
>>            DA830 support is not yet implemented.
> Sure, but if there are no actual code dependencies, I'd like to get rid of
> those depends.
> 
>>>> +u32 pruss_disable(struct device *dev, u8 pruss_num)
>>>> +{
>>>> + struct da8xx_pruss *pruss = dev_get_drvdata(dev->parent);
>>>> + da8xx_prusscore_regs h_pruss;
>>>> + u32 temp_reg;
>>>> +
>>>> + if (pruss_num == DA8XX_PRUCORE_0) {
>>>> + /* Disable PRU0  */
>>>> + h_pruss = (da8xx_prusscore_regs)
>>>> + ((u32) pruss->ioaddr + 0x7000);
>>> So it seems you're doing this in several places, and I have a few
>>> comments:
>>>
>>> - You don't need the da8xx_prusscore_regs at all.
>>> - Define the register map through a set of #define in your header file.
>>> - Use a static routine that takes the core number and returns the
>>> register map
>>> offset.
>>>
>>> Then routines like this one will look a lot more readable.
>>
>> SG -- There are a huge number of PRUSS registers. A lot of them are
>> reserved and are expected to change as development on the
>>            controller is still ongoing. 
> First of all, from what I read in your patch you're only using the CONTROL
> offset.
> 
>> If we use #defines to plot
>> all the registers, then first, there are too many array type
>> registers which will need to be duplicated.
> What I'm expecting is a small set of defines for the register offsets. You
> have 13 fields in your da8xx_prusscore_regs, you only need to define 13
> register offsets.
> 
> So, if you have a:
> 
> static u32 reg_offset(struct device *dev, u8 pru_num)
> {
> 	struct da8xx_pruss *pru = dev_get_drvdata(dev->parent);
> 
> 	switch (pru_num) {
> 	case DA8XX_PRUCORE_0:
> 		return (u32) pru->ioaddr + 0x7000;
> 	case DA8XX_PRUCORE_1:
> 		return (u32) pru->ioaddr + 0x7800;
> 	default:
> 		return 0;
> }
> 
> 
> then routines like pruss_enable (which should return an int, btw) would look
> like:
> 
> int pruss_enable(struct device *dev, u8 pruss_num)
> {
> 	u32 offset = reg_offset(dev, pruss_num);
> 
> 	if (offset == 0)
> 		return -EINVAL;
> 
> 	__raw_writel(DA8XX_PRUCORE_CONTROL_RESETVAL,
> 			offset + PRU_CORE_CONTROL);
> 
> 	return 0;
> }

All registers are memory mapped and could nicely be described by
structures (and sub-structures). Therefore we asked to considerer
structs, at least for the Pruss SocketCAN drivers. That would result in
much much clearer and better readable code. The code above would shrink to:

	__raw_writel(DA8XX_PRUCORE_CONTROL_RESETVAL,
		     &prucore[pruss_num].control);

And proper type checking would be ensured as well.

Wolfgang.



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