Re: [PATCH v2 -next 3/4] RISC-V: cacheflush: Initialize CBO variables on ACPI systems

[Sunil V L <sunilvl@ventanamicro.com>]

On Wed, Oct 04, 2023 at 10:33:31AM +0200, Andrew Jones wrote:
> On Wed, Oct 04, 2023 at 09:52:23AM +0530, Sunil V L wrote:
> > On Tue, Oct 03, 2023 at 02:50:02PM -0500, Samuel Holland wrote:
> > > On 2023-09-27 12:00 PM, Sunil V L wrote:
> > > > Using new interface to get the CBO block size information in RHCT,
> > > > initialize the variables on ACPI platforms.
> > > > 
> > > > Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
> > > > ---
> > > >  arch/riscv/mm/cacheflush.c | 37 +++++++++++++++++++++++++++++++------
> > > >  1 file changed, 31 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > > > index f1387272a551..8e59644e473c 100644
> > > > --- a/arch/riscv/mm/cacheflush.c
> > > > +++ b/arch/riscv/mm/cacheflush.c
> > > > @@ -3,7 +3,9 @@
> > > >   * Copyright (C) 2017 SiFive
> > > >   */
> > > >  
> > > > +#include <linux/acpi.h>
> > > >  #include <linux/of.h>
> > > > +#include <asm/acpi.h>
> > > >  #include <asm/cacheflush.h>
> > > >  
> > > >  #ifdef CONFIG_SMP
> > > > @@ -124,15 +126,38 @@ void __init riscv_init_cbo_blocksizes(void)
> > > >  	unsigned long cbom_hartid, cboz_hartid;
> > > >  	u32 cbom_block_size = 0, cboz_block_size = 0;
> > > >  	struct device_node *node;
> > > > +	struct acpi_table_header *rhct;
> > > > +	acpi_status status;
> > > > +	unsigned int cpu;
> > > > +
> > > > +	if (!acpi_disabled) {
> > > > +		status = acpi_get_table(ACPI_SIG_RHCT, 0, &rhct);
> > > > +		if (ACPI_FAILURE(status))
> > > > +			return;
> > > > +	}
> > > >  
> > > > -	for_each_of_cpu_node(node) {
> > > > -		/* set block-size for cbom and/or cboz extension if available */
> > > > -		cbo_get_block_size(node, "riscv,cbom-block-size",
> > > > -				   &cbom_block_size, &cbom_hartid);
> > > > -		cbo_get_block_size(node, "riscv,cboz-block-size",
> > > > -				   &cboz_block_size, &cboz_hartid);
> > > > +	for_each_possible_cpu(cpu) {
> > > > +		if (acpi_disabled) {
> > > > +			node = of_cpu_device_node_get(cpu);
> > > > +			if (!node) {
> > > > +				pr_warn("Unable to find cpu node\n");
> > > > +				continue;
> > > > +			}
> > > > +
> > > > +			/* set block-size for cbom and/or cboz extension if available */
> > > > +			cbo_get_block_size(node, "riscv,cbom-block-size",
> > > > +					   &cbom_block_size, &cbom_hartid);
> > > > +			cbo_get_block_size(node, "riscv,cboz-block-size",
> > > > +					   &cboz_block_size, &cboz_hartid);
> > > 
> > > This leaks a reference to the device node.
> > > 
> > Yep!. I missed of_node_put(). Let me add in next revision. Thanks!
> > 
> > > > +		} else {
> > > > +			acpi_get_cbo_block_size(rhct, cpu, &cbom_block_size,
> > > > +						&cboz_block_size, NULL);
> > > 
> > > This function loops through the whole RHCT already. Why do we need to call it
> > > for each CPU? Can't we just call it once, and have it do the same consistency
> > > checks as cbo_get_block_size()?
> > > 
> > > In that case, the DT path could keep the for_each_of_cpu_node() loop.
> > > 
> > I kept the same logic as DT. Basically, by passing the cpu node, we
> > will fetch the exact CPU's CBO property from RHCT. It is not clear to me
> > why we overwrite the same variable with value from another cpu and
> > whether we can return as soon as we get the CBO size for one CPU.
> > 
> > Drew, can we exit the loop if we get the CBO size for one CPU?
> 
> We want to compare the values for each CPU with the first one we find in
> order to ensure they are consistent. I think Samuel is suggesting that
> we leave the DT path here the same, i.e. keep the for_each_of_cpu_node()
> loop, and then change acpi_get_cbo_block_size() to *not* take a cpu as
> input, but rather follow the same pattern as DT, which is to loop over
> all cpus doing a consistency check against the first cpu's CBO info.
> 
Ahh OK. Thanks Drew and Samuel. Let me update as you suggested.

Thanks!
Sunil

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