[U-Boot] [PATCH 3/5] Tegra30: MMC: Add SD bus power-rail and SDMMC pad init routines

[Stephen Warren]

On 03/04/2013 04:11 PM, Tom Warren wrote:
> Stephen,
> 
> On Wed, Feb 27, 2013 at 11:08 AM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 02/27/2013 09:59 AM, Tom Warren wrote:
>>> Stephen,
>>>
>>> On Tue, Feb 26, 2013 at 4:26 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>>> On 02/26/2013 01:46 PM, Tom Warren wrote:
>>>>> T30 requires specific SDMMC pad programming, and bus power-rail bringup.
>>>>
>>>>> diff --git a/board/nvidia/cardhu/cardhu.c b/board/nvidia/cardhu/cardhu.c
>>>>
>>>>> +/*
>>>>> + * Do I2C/PMU writes to bring up SD card bus power
>>>>> + *
>>>>> + */
>>>>> +void board_sdmmc_voltage_init(void)
>>>>
>>>> We really shouldn't be adding to board files if we're remotely serious
>>>> about device tree; the whole point of DT is to remove code from the
>>>> board files, and describe the desired configuration as data in DT instead.
>>>>
>>>> This function should be replaced by regulator nodes/properties in the
>>>> device tree, and the MMC (core?) driver calling into the board-specific
>>>> regulator driver to request the desired voltages.
>>>>
>>>> But so long as we file a bug to replace this code with an explicit
>>>> regulator driver in the future, I guess it's fine for now.
>>>
>>> I'll file a bug for doing all PMU/power rail work from DT. I think it
>>> makes much more sense as a separate (non-MMC) patch.
>>
>> Yes, certainly a separate patch. Ideally it'd be implemented before
>> other code that relies on it. That's why I think we need to take a
>> higher-level look at DT support in U-Boot, rather than simply finding
>> these issue accidentally while implementing the features we already know
>> we need.
>>
>>>> BTW, I just noticed that commit f01b631 "Tegra30: Add/enable Cardhu
>>>> build (T30 reference board)" adds a file called
>>>> board/nvidia/cardhu/cardhu.c.mmc. That's a mistake, right?
>>>
>>> Yep, that's the Cardhu file I was hacking on for MMC support way back
>>> when. I can remove it in V2 of these patches, or would you prefer a
>>> single, separate patch to do that?
>>
>> Is the commit that adds that file already pulled into higher-level
>> repos? If not, I would simply rebase it to remove that file. If it has,
>> then a separate patch to delete it before this series would make sense.
>>
>>>>> diff --git a/board/nvidia/common/board.c b/board/nvidia/common/board.c
>>>>
>>>> Hmm. This seems like SoC code, not board code...
>>>>
>>>>> +void pad_init_mmc(struct tegra_mmc *reg)
>>>>> +{
>>>>> +#if defined(CONFIG_TEGRA30)
>>>>
>>>>> +     /* Set the pad drive strength for SDMMC1 or 3 only */
>>>>> +     if (offset != TEGRA_SDMMC1_BASE && offset != TEGRA_SDMMC3_BASE) {
>>>>> +             debug("%s: settings are only valid for SDMMC1/SDMMC3!\n",
>>>>> +                     __func__);
>>>>> +             return;
>>>>> +     }
>>>>
>>>> Perhaps pass in the MMC instance ID instead of the base address. That'd
>>>> avoid having to know the base addresses in this code.
>>>
>>> I still need to know if I've got a SDIO or eMMC ID, though, and I
>>> don't think the flags for that in the mmc/host structs (mmc->version,
>>> etc.) get populated until the mmc driver has done some I/O with the
>>> device (eMMC or SD-card), and I need to set up the pads before that.
>>>
>>>> In fact, just putting this code into the pinmux driver (which owns these
>>>> registers) seems like a better idea; there's no need to only do this
>>>> when the SD controller is enabled, is there?
>>>
>>> Half of these regs are in the SD controller register space
>>> (sdmemcmpctl and autocalcfg), and get reset when the controller gets
>>> reset (mmc_reset). So they need to be set each time a reset occurs. It
>>> makes sense to keep the GP SDIOCFG writes here, too.
>>>
>>> As to where the pad_init_mmc function belongs, it is SoC-specific,
>>> yes. T20 doesn't need it (no sdmemcmpctl or autocalcfg regs on T20
>>> SDMMC), and T30 and T114 use slightly different bits/values for GP
>>> SDIOCFG and sdmemcmpctl/autocalcfg. But the differences are small
>>> enough that I thought this routine should be placed in a common area,
>>> and not duplicated for each SoC, so I put it here.
>>>
>>> Do you have a suggestion of where it would be better placed?
>>
>> For the pinmux registers, I think they should be programmed by the
>> pinmux driver at the same time as the rest of the pinmux is programmed.
>
> Technically, they're not pinmux registers (PINMUX_AUX_ space), but GP
> regs (APB_MISC_GP_ space). Since the pinmux _code_ (no pinmux driver
> is used in Tegra U-Boot)

The distinction isn't relevant for this discussion. Anyway, there really
is a driver...

> for T30 is just a large table slam, I don't
> think it makes sense to add GP pad reg writes there. These pads need
> to be tuned when you've got a board w/an SD-card device hanging off of
> them. So it makes sense to have these 2 register writes here in
> pad_init_mmc(). I can take out the SDMMC1/3 test and just write both
> SDIO1CFG and SDIO3CFG, since the values are the same.

Are these value board-specific or SoC-specific? I thought that the
values came from the TRM and simply had to be set as described.

If the values are SoC-specific, I think we can just key off the
compatible value to determine whether to apply them.

If the values are board-specific, I really think we must put them into
device tree. Otherwise, we cannot claim that we have actually supported
DT in the driver - we're only doing half the job, and can't support new
boards simply by providing a new DT.

The one out might be that we could claim the current values are the
default if the DT provides no other values, even once we do define a way
for DT to provide those values. That would at least be
backwards-compatible. However, that's again going down the path of
initially defining the minimal DT binding required to get some system
running, but planning to incrementally enhance the DT binding later.
While we aren't getting strong pushback on this right now from upstream,
I can guarantee we will do very soon, so we really ought to just get
into the habit of completely defining DT bindings from the start. Still,
I suppose I won't nak this patch because of that yet.