Re: [U-Boot] [PATCH] armv8: fsl-layerscape: Add support of disabling core prefetch

[Prabhakar Kushwaha]

> -Original Message-
> From: York Sun
> Sent: Thursday, November 09, 2017 11:22 PM
> To: Prabhakar Kushwaha ; u-
> b...@lists.denx.de
> Subject: Re: [PATCH] armv8: fsl-layerscape: Add support of disabling core
> prefetch
> 
> On 11/08/2017 06:48 PM, Prabhakar Kushwaha wrote:
> > Instruction prefetch feature is by default enabled during core
> > release.
> >
> > This patch add support of disabling instruction prefetch by setting
> > core mask in PPA. Here each core mask bit represents a core and
> > prefetch is disabled at the time of core release.
> >
> > Signed-off-by: Prabhakar Kushwaha 
> > ---
> >  arch/arm/cpu/armv8/fsl-layerscape/cpu.c| 38
> ++
> >  .../armv8/fsl-layerscape/doc/README.core_prefetch  | 18 ++
> >  2 files changed, 56 insertions(+)
> >  create mode 100644 arch/arm/cpu/armv8/fsl-
> layerscape/doc/README.core_prefetch
> 
> 
> 
> > diff --git a/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
> b/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
> > new file mode 100644
> > index 000..f605a4c
> > --- /dev/null
> > +++ b/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
> > @@ -0,0 +1,18 @@
> > +Core instruction prefetch disable
> > +-
> > +To disable instruction prefetch of core; hwconfig needs to be updated.
> > +for e.g.
> > +setenv hwconfig 'fsl_ddr:bank_intlv=auto;core_prefetch:disable=0x02'
> > +
> 
> Why would one want to disable prefetch? 

There are scenario where data flow happening from device memory. 
So one want to avoid prefetching of instruction as prefetch information may be 
wrong.  
Prefetching instruction and then throwing causes performance drop. 

Hemant can you please help with more details here. 

> And environmental variables are not available for some SPL boot (eg. SD) last 
> time I check.
This feature is only required for non-boot core. Hence prefetch will never be 
disabled for core0.

--prabhakar


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Re: [U-Boot] [PATCH] armv8: fsl-layerscape: Add support of disabling core prefetch

[York Sun]

On 11/08/2017 06:48 PM, Prabhakar Kushwaha wrote:
> Instruction prefetch feature is by default enabled during core
> release.
> 
> This patch add support of disabling instruction prefetch by setting
> core mask in PPA. Here each core mask bit represents a core and
> prefetch is disabled at the time of core release.
> 
> Signed-off-by: Prabhakar Kushwaha 
> ---
>  arch/arm/cpu/armv8/fsl-layerscape/cpu.c| 38 
> ++
>  .../armv8/fsl-layerscape/doc/README.core_prefetch  | 18 ++
>  2 files changed, 56 insertions(+)
>  create mode 100644 arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch



> diff --git a/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch 
> b/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
> new file mode 100644
> index 000..f605a4c
> --- /dev/null
> +++ b/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
> @@ -0,0 +1,18 @@
> +Core instruction prefetch disable
> +-
> +To disable instruction prefetch of core; hwconfig needs to be updated.
> +for e.g.
> +setenv hwconfig 'fsl_ddr:bank_intlv=auto;core_prefetch:disable=0x02'
> +

Why would one want to disable prefetch? And environmental variables are
not available for some SPL boot (eg. SD) last time I check.

York
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[U-Boot] [PATCH] armv8: fsl-layerscape: Add support of disabling core prefetch

[Prabhakar Kushwaha]

Instruction prefetch feature is by default enabled during core
release.

This patch add support of disabling instruction prefetch by setting
core mask in PPA. Here each core mask bit represents a core and
prefetch is disabled at the time of core release.

Signed-off-by: Prabhakar Kushwaha 
---
 arch/arm/cpu/armv8/fsl-layerscape/cpu.c| 38 ++
 .../armv8/fsl-layerscape/doc/README.core_prefetch  | 18 ++
 2 files changed, 56 insertions(+)
 create mode 100644 arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch

diff --git a/arch/arm/cpu/armv8/fsl-layerscape/cpu.c 
b/arch/arm/cpu/armv8/fsl-layerscape/cpu.c
index ab5d76e..d082629 100644
--- a/arch/arm/cpu/armv8/fsl-layerscape/cpu.c
+++ b/arch/arm/cpu/armv8/fsl-layerscape/cpu.c
@@ -29,6 +29,7 @@
 #include 
 #endif
 #include 
+#include 
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -494,6 +495,41 @@ static inline int check_psci(void)
return 0;
 }
 
+static void config_core_prefetch(void)
+{
+   char *buf = NULL;
+   char buffer[HWCONFIG_BUFFER_SIZE];
+   const char *prefetch_arg = NULL;
+   size_t arglen;
+   unsigned int mask;
+   struct pt_regs regs;
+
+   if (env_get_f("hwconfig", buffer, sizeof(buffer)) > 0)
+   buf = buffer;
+
+   prefetch_arg = hwconfig_subarg_f("core_prefetch", "disable",
+, buf);
+
+   if (prefetch_arg) {
+   mask = simple_strtoul(prefetch_arg, NULL, 0) & 0xff;
+   if (mask & 0x1) {
+   printf("Core0 prefetch can't be disabled\n");
+   return;
+   }
+
+#define SIP_PREFETCH_DISABLE_64 0xC200FF13
+   regs.regs[0] = SIP_PREFETCH_DISABLE_64;
+   regs.regs[1] = mask;
+   smc_call();
+
+   if (regs.regs[0])
+   printf("Prefetch disable config failed for mask ");
+   else
+   printf("Prefetch disable config passed for mask ");
+   printf("0x%x\n", mask);
+   }
+}
+
 int arch_early_init_r(void)
 {
 #ifdef CONFIG_SYS_FSL_ERRATUM_A009635
@@ -521,6 +557,8 @@ int arch_early_init_r(void)
fsl_rgmii_init();
 #endif
 
+   config_core_prefetch();
+
 #ifdef CONFIG_SYS_HAS_SERDES
fsl_serdes_init();
 #endif
diff --git a/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch 
b/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
new file mode 100644
index 000..f605a4c
--- /dev/null
+++ b/arch/arm/cpu/armv8/fsl-layerscape/doc/README.core_prefetch
@@ -0,0 +1,18 @@
+Core instruction prefetch disable
+-
+To disable instruction prefetch of core; hwconfig needs to be updated.
+for e.g.
+setenv hwconfig 'fsl_ddr:bank_intlv=auto;core_prefetch:disable=0x02'
+
+Here 0x02 can be replaced with any valid value. It represents 64 bit mask.
+The 64-bit Mask has one bit for each core.
+Mask[0] = core0
+Mask[1] = core1
+Mask[2] = core2
+etc
+If the bit is set ('b1) in the mask, then prefetch is disabled for
+that core when it is released from reset.
+core0 prefetch should not be disabled.
+
+Once disabled, prefetch remains disabled until the next reset.
+There is no function to re-enable prefetch.
-- 
2.7.4

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