linux-kernel - Re: [RFC PATCH v1 08/21] RISC-V: ACPI: RHCT: Add function to get CBO block sizes

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Message-ID: <ZMzF6e8jjGY2YNjm@sunil-laptop>
Date:   Fri, 4 Aug 2023 15:03:29 +0530
From:   Sunil V L <sunilvl@...tanamicro.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-doc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Anup Patel <anup@...infault.org>,
        Marc Zyngier <maz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Robert Moore <robert.moore@...el.com>,
        Haibo Xu <haibo1.xu@...el.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Atish Kumar Patra <atishp@...osinc.com>
Subject: Re: [RFC PATCH v1 08/21] RISC-V: ACPI: RHCT: Add function to get CBO
 block sizes

On Fri, Aug 04, 2023 at 09:00:45AM +0300, Andy Shevchenko wrote:
> On Thu, Aug 03, 2023 at 11:29:03PM +0530, Sunil V L wrote:
> > CBO related block size in ACPI is provided by RHCT. Add
> > support to read the CMO node in RHCT to get this information.
> 
> ...
> 
> > +	if (!table) {
> 
> Why not positive conditional?
> 
Sure.

> > +		rhct = (struct acpi_table_rhct *)acpi_get_rhct();
> > +		if (!rhct)
> > +			return -ENOENT;
> > +	} else {
> > +		rhct = (struct acpi_table_rhct *)table;
> > +	}
> 
> ...
> 
> > +	end = ACPI_ADD_PTR(struct acpi_rhct_node_header, rhct, rhct->header.length);
> 
> > +
> 
> Blank line here is not needed.
> 
Okay.

> > +	for (node = ACPI_ADD_PTR(struct acpi_rhct_node_header, rhct, rhct->node_offset);
> > +	     node < end;
> > +	     node = ACPI_ADD_PTR(struct acpi_rhct_node_header, node, node->length)) {
> 
> > +			for (int i = 0; i < hart_info->num_offsets; i++) {
> > +				ref_node = ACPI_ADD_PTR(struct acpi_rhct_node_header,
> > +							rhct, hart_info_node_offset[i]);
> > +				if (ref_node->type == ACPI_RHCT_NODE_TYPE_CMO) {
> > +					cmo_node = ACPI_ADD_PTR(struct acpi_rhct_cmo_node,
> > +								ref_node, size_hdr);
> > +					if (cbom_size)
> > +						*cbom_size = 1 << cmo_node->cbom_size;
> > +
> > +					if (cboz_size)
> > +						*cboz_size = 1 << cmo_node->cboz_size;
> > +
> > +					if (cbop_size)
> > +						*cbop_size = 1 << cmo_node->cbop_size;
> 
> BIT() in all three cases?
>
Sure.
 
> But how you guarantee it will not overflow? I mean who prevents cboX_size to be
> bigger than 30 (note also that 31 in your case is Undefined Behaviour in
> accordance with the C standard).
> 
Good catch!. Let me add a check that the value is not more than 30.

Thanks!
Sunil