[U-Boot] Cache alignment warnings on Tegra (ARM)

[Marek Vasut]

Dear Thierry Reding,

> On Fri, Sep 14, 2012 at 08:53:32AM -0700, Simon Glass wrote:
> > Hi,
> > 
> > On Wed, Sep 12, 2012 at 4:42 PM, Marek Vasut <marex at denx.de> wrote:
> > > Dear Stephen Warren,
> > > 
> > >> On 09/12/2012 04:38 PM, Marek Vasut wrote:
> > >> > Dear Stephen Warren,
> > >> > 
> > >> >> On 09/12/2012 10:19 AM, Tom Warren wrote:
> > >> >>> Folks,
> > >> >>> 
> > >> >>> Stephen Warren has posted an internal bug regarding the cache
> > >> >>> alignment 'warnings' seen on Tegra20 boards when accessing MMC.
> > >> >>> Here's the gist:
> > >> >>> 
> > >> >>> Executing "mmc dev 0" still yields cache warnings:
> > >> >>> 
> > >> >>> Tegra20 (Harmony) # mmc dev 0
> > >> >>> ERROR: v7_dcache_inval_range- stop address is not aligned-
> > >> >>> 0x3fb69908 mmc0 is current device
> > >> >> 
> > >> >> ...
> > >> >> 
> > >> >>> There have been patches in the past (IIRC) that have tried to
> > >> >>> ensure all callers (FS, MMC driver, USB driver, etc.) force their
> > >> >>> buffers to the appropriate alignment, but I don't know that we
> > >> >>> can ever correct every instance, now or in the future.
> > >> >>> 
> > >> >>> Can we start a discussion about what we can do about this warning?
> > >> >>> Adding an appropriate #ifdef
> > >> >>> (CONFIG_SYS_NO_CACHE_ALIGNMENT_WARNINGS, etc.) where Stephen put
> > >> >>> his #if 0's would be one approach, or changing the printf() to a
> > >> >>> debug(), perhaps. As far as I can tell, these alignment 'errors'
> > >> >>> don't seem to produce bad data in the transfer.
> > >> >> 
> > >> >> I don't think simply turning off the warning is the correct
> > >> >> approach; I believe they represent real problems that can in fact
> > >> >> cause data corruption. I don't believe we have any choice other
> > >> >> than to fully solve the root-cause.
> > 
> > Yes I agree, and I think it is pretty close - certainly much better
> > than it used to be. The good thing about them being annoying is that
> > they will likely get fixed :-)
> 
> I think I traced this to the copying of CSD a while back. The problem is
> that the transferred buffer is 8 bytes, so there's no way to make it
> aligned properly. Unfortunately the entailing discussion did not yield a
> solution at the time.

And how exactly does the MMC bounce buffer not help here?

> Thierry

Best regards,
Marek Vasut