Driver complaint to SD Host Controller Specification 3.0

[André Marques]

Hello mudit,

Às 15:06 de 26-05-2016, Mudit Jain escreveu:
> Hi Sebastian & Andre,
>
> In the last IRC meeting, Gedare had mentioned that you have previously 
> worked on the SD card driver.
>
> I was working on the SD Card driver for Rpi.
>
> I was going through the driver code that has been ported. I was able 
> to browse and get a top level overview regarding the ported driver 
> using the documentation for the APIs used from FreeBSD.
>
> The driver is working for the powerpc/qoriq BSP.
>
> I wanted to know which SDHC is present on that BSP and to which 
> specification was the driver tailored to?
>
> RPi has a SD host controller that is complaint to Specification 3.0. 
> Thus I was following this link :
> https://www.sdcard.org/downloads/pls/pdf/partA2_300.pdf.
>
> Andre, were the previous commits regarding the reset logic done based 
> on this specification ? I wanted to clarify that that function logics 
> that are to be implemented will be based on this specification ?
>
> Thanks
> Mudit
>
>

The driver in libbsd is from what i remember compliant with the version 
3.0 of the simplified specs (it was the version I followed, and the 
driver seemed to match it). However, each SD controller have their 
quirks (the cards may also have their own), hence why in some parts of 
the libbsd drivers there are some ifdef guards with specific code for 
clock setting, card reset sequence, data transfer,... for the 
powerpc/qoric BSP. The specification in only a guideline.

As for more reference material, you may compare/look at the 
specification and its implementation (in the libbsd sdhci driver) with 
some existing driver for the raspberry sd host controller (e.g.: 
https://github.com/jncronin/rpi-boot/blob/master/emmc.c). The ideal 
would be to have the raspberry pi's sd host controller documentation 
from arasan, but it is not freely available.

--André Marques