Re: [PATCH 0/4] add minimal bcm2835-sdram driver

[Stefan Wahren]

Hi,

> Martin Sperl <kernel@xxxxxxxxxxxxxxxx> hat am 12. Mai 2016 um 17:28
> geschrieben:
> 
> 
> 
> > On 12.05.2016, at 16:50, Stefan Wahren <stefan.wahren@xxxxxxxx> wrote:
> > 
> > Hi Martin,
> > 
> >> kernel@xxxxxxxxxxxxxxxx hat am 12. Mai 2016 um 14:38 geschrieben:
> >> 
> >> 
> >> From: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
> >> 
> >> As the sdram clock is a critical clock to the system
> >> the minimal bcm2835-sdram driver claims (and enables)
> >> this clock and also exposes the corresponding sdram
> >> registers via debugfs.
> > 
> > sounds like this driver should fix an clock handling issue. Unfortunately
> > this
> > isn't a solution in case the driver is disabled.
> Unfortunately there is no way around this - the driver has
> to be enabled so that the sdram clock or the parent pll,
> which typically is plld_core, never gets disabled.
> 
> The only other option would be marking the clock as critical
> for those legacy drivers.

i would prefer this option. Since this would be more a fix we could get this
faster in, it's more clear why we are doing that and less to review.

Did i miss a drawback?

Stefan

> 
> See also the discussions around the clock register for the
> sdram clock, where we have the ânormalâ clock and some
> pll as well - even if the ânormalâ clock is disabled, 
> then clearing the sdram register (or the parent) freezes
> the system.
> 
> > 
> > Does the GPU firmware handle the SDRAM controller or is it initialized by
> > bootcode?
> > 
> 
> AFAIK it is enabled in bootcode.bin and - as of now - the firmware
> updates refresh cycles when SOC temperatures change.
> FW checks every 30 seconds unless there is a key set in config.txt,
> which - supposedly - produces a slight impact every 30 seconds to
> the system.
> 
> Martin