On SAMA7G5 the prescaler part of master clock has been implemented as a
changeable one. Everytime the prescaler is changed the PMC_SR.MCKRDY bit
must be polled. Value 1 for PMC_SR.MCKRDY means the prescaler update is
done. Driver polls for this bit until it becomes 1. On SAMA7G5 it has
been discovered that in some conditions the PMC_SR.MCKRDY is not rising
but the rate it provides it's stable. The workaround is to add a timeout
when polling for PMC_SR.MCKRDY. At the moment, for SAMA7G5, the prescaler
will be removed from Linux clock tree as all the frequencies for CPU could
be obtained from PLL and also there will be less overhead when changing
frequency via DVFS.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20211011112719.3951784-14-claudiu.beznea@microchip.com
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
SAMA7G5 supports DVFS by changing cpuck. On SAMA7G5 mck0 shares the same
parent with cpuck as seen in the following clock tree:
+----------> cpuck
|
FRAC PLL ---> DIV PLL -+-> DIV ---> mck0
mck0 could go b/w 32KHz and 200MHz on SAMA7G5. To avoid mck0 overclocking
while changing FRAC PLL or DIV PLL the commit implements a notifier for
mck0 which applies a safe divider to register (maximum value of the divider
which is 5) on PRE_RATE_CHANGE events (such that changes on PLL to not
overclock mck0) and sets the maximum allowed rate on POST_RATE_CHANGE
events.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20211011112719.3951784-13-claudiu.beznea@microchip.com
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
SAM9X60's PLL which is also part of SAMA7G5 is composed of 2 parts:
one fractional part and one divider. On SAMA7G5 the CPU PLL could be
changed at run-time to implement DVFS. The hardware clock tree on
SAMA7G5 for CPU PLL is as follows:
+---- div1 ----------------> cpuck
|
FRAC PLL ---> DIV PLL -+-> prescaler ---> div0 ---> mck0
The div1 block is not implemented in Linux; on prescaler block it has
been discovered a bug on some scenarios and will be removed from Linux
in next commits. Thus, the final clock tree that will be used in Linux
will be as follows:
+-----------> cpuck
|
FRAC PLL ---> DIV PLL -+-> div0 ---> mck0
It has been proposed in [1] to not introduce a new CPUFreq driver but
to overload the proper clock drivers with proper operation such that
cpufreq-dt to be used. To accomplish this DIV PLL and div0 implement
clock notifiers which applies safe dividers before FRAC PLL is changed.
The current commit treats only the DIV PLL by adding a notifier that
sets a safe divider on PRE_RATE_CHANGE events. The safe divider is
provided by initialization clock code (sama7g5.c). The div0 is treated
in next commits (to keep the changes as clean as possible).
[1] https://lore.kernel.org/lkml/20210105104426.4tmgc2l3vyicwedd@vireshk-i7/
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20211011112719.3951784-12-claudiu.beznea@microchip.com
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Register CPU clock as being the master clock prescaler. This would
be used by DVFS. The block schema of SAMA7G5's PMC contains also a divider
between master clock prescaler and CPU (PMC_CPU_RATIO.RATIO) but the
frequencies supported by SAMA7G5 could be directly received from
CPUPLL + master clock prescaler and the extra divider would do no work in
case it would be enabled.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/1605800597-16720-12-git-send-email-claudiu.beznea@microchip.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
