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Subject: Re: [RFC PATCH 10/36] ACPI / MPAM: Parse the MPAM table
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
 Rob Herring <robh@kernel.org>, Ben Horgan <ben.horgan@arm.com>,
 Rohit Mathew <rohit.mathew@arm.com>,
 Shanker Donthineni <sdonthineni@nvidia.com>, Zeng Heng
 <zengheng4@huawei.com>, Lecopzer Chen <lecopzerc@nvidia.com>,
 Carl Worth <carl@os.amperecomputing.com>,
 shameerali.kolothum.thodi@huawei.com,
 D Scott Phillips OS <scott@os.amperecomputing.com>, lcherian@marvell.com,
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References: <20250711183648.30766-1-james.morse@arm.com>
 <20250711183648.30766-11-james.morse@arm.com>
 <20250716180725.0000452d@huawei.com> <20250728110849.00004062@huawei.com>
Content-Language: en-GB
From: James Morse <james.morse@arm.com>
In-Reply-To: <20250728110849.00004062@huawei.com>
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Hi Jonathan,

On 28/07/2025 11:08, Jonathan Cameron wrote:
>>> +static struct acpi_table_header *get_table(void)
>>> +{
>>> +	struct acpi_table_header *table;
>>> +	acpi_status status;
>>> +
>>> +	if (acpi_disabled || !system_supports_mpam())
>>> +		return NULL;
>>> +
>>> +	status = acpi_get_table(ACPI_SIG_MPAM, 0, &table);
>>> +	if (ACPI_FAILURE(status))
>>> +		return NULL;
>>> +
>>> +	if (table->revision != 1)
> 
> Missing an acpi_put_table()

Oops,


> I'm messing around with ACQUIRE() that is queued in the CXL tree
> for the coming merge window and noticed this.
> https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git/log/?h=for-6.17/cleanup-acquire

(not more C++!)


> Interestingly this is a new corner case where we want conditional locking
> style handling but with return_ptr() style handling. Maybe too much of a niche
> to bother with infrastructure.
> 
> Worth noting though that one layer up it is probably worth something like:
> 
> DEFINE_FREE(acpi_table_mpam, struct acpi_table_header *, if (_T) acpi_put_table(_T));
> 
> That enables nice clean code like:
> 
> 
> static int __init acpi_mpam_parse(void)
> {
> 	struct acpi_table_header *mpam = __free(acpi_table_mpam) = get_table();
> 
> 	if (!mpam)
> 		return 0;
> 
> 	return _parse_table;
> }

I've got bits of that from your PPTT suggestions. I ended up folding the get_table()
helper in here.

count_msc() gets the same treatment and the cleanup thing lets _count_msc() be folded into it.


Thanks,

James


> This series was big enough that I'm spinning a single 'suggested changes'
> patch on top of it that includes stuff like this.  Might take another day or so.
> 
> Jonathan