Re: [PATCH 04/14] ARM: OMAP2+: Add function for configuring GPMC settings

[Jon Hunter <jon-hunter@ti.com>]

On 02/28/2013 11:33 PM, Philip, Avinash wrote:
> On Thu, Feb 28, 2013 at 22:42:37, Hunter, Jon wrote:
>>
>> On 02/28/2013 09:52 AM, Jon Hunter wrote:
>>>
>>> On 02/28/2013 12:05 AM, Philip, Avinash wrote:
>>>> On Tue, Feb 26, 2013 at 23:00:31, Hunter, Jon wrote:
>>>>> The GPMC has various different configuration options such as bus-width,
>>>>> synchronous or asychronous mode selection, burst mode options etc.
>>>>> Currently, there is no common function for configuring these options and
>>>>> various devices set these options by either programming the GPMC CONFIG1
>>>>> register directly or by calling gpmc_cs_configure() to set some of the
>>>>> options.
>>>>>
>>>>> Add a new function for configuring all of the GPMC options. Having a common
>>>>> function for configuring this options will simplify code and ease the
>>>>> migration to device-tree.
>>>>>
>>>>> Signed-off-by: Jon Hunter <jon-hunter@ti.com>
>>>>> ---
>>>>>  arch/arm/mach-omap2/gpmc.c |   65 ++++++++++++++++++++++++++++++++++++++++++++
>>>>>  arch/arm/mach-omap2/gpmc.h |    6 ++++
>>>>>  2 files changed, 71 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm/mach-omap2/gpmc.c b/arch/arm/mach-omap2/gpmc.c
>>>>> index 465cac9..fb8dfd2 100644
>>>>> --- a/arch/arm/mach-omap2/gpmc.c
>>>>> +++ b/arch/arm/mach-omap2/gpmc.c
>>>>> @@ -1137,6 +1137,71 @@ int gpmc_calc_timings(struct gpmc_timings *gpmc_t,
>>>>>  	return 0;
>>>>>  }
>>>>>  
>>>>> +int gpmc_cs_program_settings(int cs, struct gpmc_settings *p)
>>>>> +{
>>>>> +	u32 config1;
>>>>> +
>>>>> +	if ((!p->device_width) || (p->device_width > GPMC_DEVWIDTH_16BIT)) {
>>>>> +		pr_err("%s: invalid width %d!", __func__, p->device_width);
>>>>> +		return -EINVAL;
>>>>> +	}
>>>>> +
>>>>> +	/* Address-data multiplexing not supported for NAND devices */
>>>>> +	if (p->device_nand && p->mux_add_data) {
>>>>> +		pr_err("%s: invalid configuration!\n", __func__);
>>>>> +		return -EINVAL;
>>>>> +	}
>>>>> +
>>>>> +	/* Page/burst mode supports lengths of 4, 8 and 16 bytes */
>>>>> +	if (p->burst_read || p->burst_write) {
>>>>> +		switch (p->burst_len) {
>>>>> +		case GPMC_BURST_4:
>>>>> +		case GPMC_BURST_8:
>>>>> +		case GPMC_BURST_16:
>>>>> +			break;
>>>>> +		default:
>>>>> +			pr_err("%s: invalid page/burst-length (%d)\n",
>>>>> +			       __func__, p->burst_len);
>>>>> +			return -EINVAL;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	if ((p->wait_on_read || p->wait_on_write) &&
>>>>> +	    (p->wait_pin > gpmc_nr_waitpins)) {
>>>>> +		pr_err("%s: invalid wait-pin (%d)\n", __func__, p->wait_pin);
>>>>> +		return -EINVAL;
>>>>> +	}
>>>>> +
>>>>> +	config1 = GPMC_CONFIG1_DEVICESIZE((p->device_width - 1));
>>>>
>>>> Can you consider read_modify approach?
>>>
>>> I was purposely trying to avoid that. The intent here is to program all
>>> the settings and get away from any boot-loader dependencies. If we use a
>>> read-modify approach then it will never be clear in the kernel what
>>> should actually be programmed.
>>
>> By the way, it would be good to know what your motivation for this is.
>>
>> My goal is for all gpmc settings to eventually live in the DT blob and
>> there be no dependency on the bootloader whatsoever. That may mean that
>> settings are re-programmed again by the kernel but IMO that is best.
> 
> Yes I understood now and the right thing to do.
> Suggested read modify approach because of some confusion as GPMC_CONFIG1 is already
> modified in gpmc_cs_set_timings() and is called from omap2_nand_gpmc_retime().
> So the data modified in gpmc_cs_set_timings() will lost (not significant)
> May be better and cleaner solution is to remove GPMC_CONFIG1 modification in
> gpmc_cs_set_timings() also.

Actually that is a good point. There are some timings in CONFIG1 that
are not being configured in gpmc_cs_program_settings() but
gpmc_cs_set_timings(). I had left it this way intentionally to keep
timings together, which makes sense for where gpmc clock could change at
run time. However, this means that gpmc_cs_program_settings() needs to
be called before gpmc_cs_set_timings(). Really this is no different to
how the code was before, because the code was writing directly to
CONFIG1 and now we have a function.

So the intent is for gpmc_cs_program_settings() to only be called once
for a given device and then gpmc_cs_set_timings() be called whenever the
timings need to be updated. May be I can updated the kernel-doc for
gpmc_cs_program_settings() to reflect this. Let me know if you have any
other concerns with this.

Cheers
Jon