[coreboot] Add coreboot storage driver

[Andrey Petrov]

Hi,

On 02/13/2017 11:16 AM, Nico Huber wrote:
> On 13.02.2017 08:19, Andrey Petrov wrote:
>> For example Apollolake is struggling to finish firmware boot with all
>> the whistles and bells (vboot, tpm and our friendly, ever-vigilant TXE)
>> under one second.
> Can you provide exhaustive figures, which part of this system's boot
> process takes how long? That would make it easier to reason about where
> "parallelism" would provide a benefit.

Such data is available.  Here is a boot chart I drew few months back:
http://imgur.com/a/huyPQ

I color-coded different work types. Some blocks are coded incorrectly 
please bear with me).

So what we can see is that everything is serial and there is great deal 
of waiting. For that specific SDHCI case you can see "Storage device 
initialization" that is happening in depthcharge. That is CMD1 that you 
need keep on sending to the controller. As you can see, it completes in 
130ms. Unfortunately you really can't just send CMD1 and go about your 
business. You need to poll readiness status and keep on sending CMD1 
again and again. Also, it is not always 130ms. It tends to vary and 
worst case we seen was over 300ms. Another one is "kernel read", which 
is pure IO and takes 132ms. If you invest some 300ms in training the 
link (has to happen on every boot on every board) to HS400 you can read 
it in just 10ms. Naturally you can't see HS400 in the picture because 
enabling it late in the boot flow would be counter productive.

That's essentially the motivation to why we are looking into starting 
this CMD1 and HS400 link training as early as possible. However fixing 
this particular issue is just a "per-platform" fix. I was hoping we 
could come up with a model that adds parallelism as a generic reusable 
feature not just a quick hack.

Andrey