[U-Boot] [PATCH v2 8/9] tegra: add SPI SLINK driver

[Stephen Warren <swarren@wwwdotorg.org>]

On 01/14/2013 09:33 PM, Allen Martin wrote:
> On Mon, Jan 14, 2013 at 10:49:53AM -0800, Stephen Warren wrote:
>> On 01/12/2013 09:56 AM, Simon Glass wrote:
>>> Hi,
>>>
>>> On Sat, Jan 12, 2013 at 1:07 AM, Allen Martin <amartin@nvidia.com> wrote:
>>>> Add driver for tegra SPI "SLINK" style driver.  This controller is
>>>> similar to the tegra20 SPI "SFLASH" controller.  The difference is
>>>> that the SLINK controller is a genernal purpose SPI controller and the
>>>> SFLASH controller is special purpose and can only talk to FLASH
>>>> devices.  In addition there are potentially many instances of an SLINK
>>>> controller on tegra and only a single instance of SFLASH.  Tegra20 is
>>>> currently ths only version of tegra that instantiates an SFLASH
>>>> controller.
>>>>
>>>> This driver supports basic PIO mode of operation and is configurable
>>>> (CONFIG_OF_CONTROL) to be driven off devicetree bindings.  Up to 4
>>>> devices per controller may be attached, although typically only a
>>>> single chip select line is exposed from tegra per controller so in
>>>> reality this is usually limited to 1.
>>>>
>>>> To enable this driver, use CONFIG_TEGRA_SLINK

>>>> +void spi_init(void)
>>>> +{
>>>> +       int node = 0, i;
>>>> +       struct tegra_spi_ctrl *ctrl;
>>>
>>> blank line here
>>>
>>>> +       for (i = 0; i < CONFIG_TEGRA_SLINK_CTRLS; i++) {
>>>> +               ctrl = &spi_ctrls[i];
>>>> +#ifdef CONFIG_OF_CONTROL
>>>> +               node = fdtdec_next_compatible(gd->fdt_blob, node,
>>>> +                                             COMPAT_NVIDIA_TEGRA20_SLINK);
>>>> +               if (!node)
>>>> +                       break;
>>>
>>> I think you should be using fdtdec_find_aliases_for_id() so that aliases work.
>>
>> I strongly believe we shouldn't be using aliases for enumeration, which
>> is what fdtdec_find_aliases_for_id() does, IIRC. Instead, we should
>> enumerate all the devices in the correct fashion, and then apply aliases
>> as a separate step if they exists. Hence, I believe it's not correct to
>> use fdtdec_find_aliases_for_id() anywhere.
> 
> I'm a bit confused about the usage of fdt aliases in u-boot.  My
> understanding of aliases is that they are intended to give drivers
> hints about device naming.  Since u-boot doesn't really name devices,
> what are aliases supposed to do?

Most U-Boot command use IDs to identify devices/interfaces, e.g. in
"ext2load mmc 0:1", the "0" means MMC instance #0. The instance number
is parsed out from the end of the alias name.