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hw/ppc: Support for an IBM PPE42 CPU decrementer

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The IBM PPE42 processors support a 32-bit decrementer
that can raise an external interrupt when DEC[0]
transitions from a 0 to a -1 (a non-negative value to a
negative value).  It also continues decrementing
even after this condition is met.

The BookE timer is slightly different in that it
raises an interrupt when the DEC value reaches 0
and stops decrementing at that point.

Support a PPE42 version of the BookE timer by
adding a new PPC_TIMER_PPE flag that has the timer
code look for the transition from a non-negative value
to a negative value and allows the value to
continue decrementing.

Signed-off-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Link: https://lore.kernel.org/r/20250925201758.652077-8-milesg@linux.ibm.com
Message-ID: <20250925201758.652077-8-milesg@linux.ibm.com>
This commit is contained in:
Glenn Miles
2025-09-28 23:39:19 +05:30
committed by Harsh Prateek Bora
parent f7ec91c239
commit 7197f6f7ba
2 changed files with 7 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
hw/ppc/ppc_booke.c
+6 -1
View File
@@ -352,7 +352,12 @@ void ppc_booke_timers_init(PowerPCCPU *cpu, uint32_t freq, uint32_t flags)
booke_timer = g_new0(booke_timer_t, 1);
cpu->env.tb_env = tb_env;
tb_env->flags = flags | PPC_TIMER_BOOKE | PPC_DECR_ZERO_TRIGGERED;
if (flags & PPC_TIMER_PPE) {
/* PPE's use a modified version of the booke behavior */
tb_env->flags = flags | PPC_DECR_UNDERFLOW_TRIGGERED;
} else {
tb_env->flags = flags | PPC_TIMER_BOOKE | PPC_DECR_ZERO_TRIGGERED;
}
tb_env->tb_freq = freq;
tb_env->decr_freq = freq;
include/hw/ppc/ppc.h
+1
View File
@@ -52,6 +52,7 @@ struct ppc_tb_t {
#define PPC_DECR_UNDERFLOW_LEVEL (1 << 4) /* Decr interrupt active when
* the most significant bit is 1.
*/
#define PPC_TIMER_PPE (1 << 5) /* Enable PPE support */
uint64_t cpu_ppc_get_tb(ppc_tb_t *tb_env, uint64_t vmclk, int64_t tb_offset);
void cpu_ppc_tb_init(CPUPPCState *env, uint32_t freq);