Re: [PATCH 06/18] cxl: Add callback to parse the DSMAS subtables from CDAT

[Dave Jiang <dave.jiang@intel.com>]

On 2/9/23 6:29 AM, Jonathan Cameron wrote:
> On Mon, 06 Feb 2023 13:50:15 -0700
> Dave Jiang <dave.jiang@intel.com> wrote:
> 
>> Provide a callback function to the CDAT parser in order to parse the Device
>> Scoped Memory Affinity Structure (DSMAS). Each DSMAS structure contains the
>> DPA range and its associated attributes in each entry. See the CDAT
>> specification for details.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> Hi Dave,
> 
> A few minor questions / comments inline,
> 
> Jonathan
> 
>> ---
>>   drivers/cxl/core/cdat.c |   25 +++++++++++++++++++++++++
>>   drivers/cxl/core/port.c |    2 ++
>>   drivers/cxl/cxl.h       |   11 +++++++++++
>>   drivers/cxl/port.c      |    8 ++++++++
>>   4 files changed, 46 insertions(+)
>>
>> diff --git a/drivers/cxl/core/cdat.c b/drivers/cxl/core/cdat.c
>> index be09c8a690f5..f9a64a0f1ee4 100644
>> --- a/drivers/cxl/core/cdat.c
>> +++ b/drivers/cxl/core/cdat.c
>> @@ -96,3 +96,28 @@ int cdat_table_parse_dslbis(void *table, cdat_tbl_entry_handler handler, void *a
>>   	return cdat_table_parse_entries(ACPI_CDAT_TYPE_DSLBIS, header, &proc, 0);
>>   }
>>   EXPORT_SYMBOL_NS_GPL(cdat_table_parse_dslbis, CXL);
>> +
>> +int cxl_dsmas_parse_entry(struct acpi_cdat_header *header, void *arg)
>> +{
>> +	struct cxl_port *port = (struct cxl_port *)arg;
>> +	struct dsmas_entry *dent;
>> +	struct acpi_cdat_dsmas *dsmas;
>> +
>> +	if (header->type != ACPI_CDAT_TYPE_DSMAS)
>> +		return -EINVAL;
>> +
>> +	dent = devm_kzalloc(&port->dev, sizeof(*dent), GFP_KERNEL);
>> +	if (!dent)
>> +		return -ENOMEM;
>> +
>> +	dsmas = (struct acpi_cdat_dsmas *)((unsigned long)header + sizeof(*header));
> 
> I'd prefer header + 1

It's simpler. Will update.

> 
> 
>> +	dent->handle = dsmas->dsmad_handle;
>> +	dent->dpa_range.start = dsmas->dpa_base_address;
>> +	dent->dpa_range.end = dsmas->dpa_base_address + dsmas->dpa_length - 1;
>> +
>> +	mutex_lock(&port->cdat.dsmas_lock);
>> +	list_add_tail(&dent->list, &port->cdat.dsmas_list);
>> +	mutex_unlock(&port->cdat.dsmas_lock);
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_dsmas_parse_entry, CXL);
>> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
>> index fe78daf7e7c8..2b27319cfd42 100644
>> --- a/drivers/cxl/core/port.c
>> +++ b/drivers/cxl/core/port.c
>> @@ -660,6 +660,8 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
>>   	device_set_pm_not_required(dev);
>>   	dev->bus = &cxl_bus_type;
>>   	dev->type = &cxl_port_type;
>> +	INIT_LIST_HEAD(&port->cdat.dsmas_list);
>> +	mutex_init(&port->cdat.dsmas_lock);
>>   
>>   	return port;
>>   
>> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
>> index 839a121c1997..1e5e69f08480 100644
>> --- a/drivers/cxl/cxl.h
>> +++ b/drivers/cxl/cxl.h
>> @@ -8,6 +8,7 @@
>>   #include <linux/bitfield.h>
>>   #include <linux/bitops.h>
>>   #include <linux/log2.h>
>> +#include <linux/list.h>
>>   #include <linux/io.h>
>>   #include <linux/acpi.h>
>>   
>> @@ -520,6 +521,8 @@ struct cxl_port {
>>   	struct cxl_cdat {
>>   		void *table;
>>   		size_t length;
>> +		struct list_head dsmas_list;
>> +		struct mutex dsmas_lock; /* lock for dsmas_list */
> 
> I'm curious, what might race with the dsmas_list changing and hence what is lock for?

It should be dropped. The latest implementation has all the access 
during port probe so no longer needing locking.

> 
>>   	} cdat;
>>   	bool cdat_available;
>>   };
>> @@ -698,6 +701,12 @@ static inline struct cxl_pmem_region *to_cxl_pmem_region(struct device *dev)
>>   }
>>   #endif
>>   
>> +struct dsmas_entry {
>> +	struct list_head list;
>> +	struct range dpa_range;
>> +	u16 handle;
> 
> handle is 1 byte in the spec. Why larger here?

It should be u8. Oops. Thanks for the catch.


> 
>> +};
>> +
>>   typedef int (*cdat_tbl_entry_handler)(struct acpi_cdat_header *header, void *arg);
>>   
>>   u8 cdat_table_checksum(u8 *buffer, u32 length);
>> @@ -706,6 +715,8 @@ int cdat_table_parse_dsmas(void *table, cdat_tbl_entry_handler handler,
>>   int cdat_table_parse_dslbis(void *table, cdat_tbl_entry_handler handler,
>>   			    void *arg);
>>   
>> +int cxl_dsmas_parse_entry(struct acpi_cdat_header *header, void *arg);
>> +
>>   /*
>>    * Unit test builds overrides this to __weak, find the 'strong' version
>>    * of these symbols in tools/testing/cxl/.
>> diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
>> index 5453771bf330..b1da73e99bab 100644
>> --- a/drivers/cxl/port.c
>> +++ b/drivers/cxl/port.c
>> @@ -61,6 +61,14 @@ static int cxl_port_probe(struct device *dev)
>>   		if (rc)
>>   			return rc;
>>   
>> +		if (port->cdat.table) {
>> +			rc = cdat_table_parse_dsmas(port->cdat.table,
>> +						    cxl_dsmas_parse_entry,
>> +						    (void *)port);
>> +			if (rc < 0)
>> +				dev_dbg(dev, "Failed to parse DSMAS: %d\n", rc);
>> +		}
>> +
>>   		rc = cxl_hdm_decode_init(cxlds, cxlhdm);
>>   		if (rc)
>>   			return rc;
>>
>>
>