linux-kernel - Re: [PATCH RFC v2 03/18] cxl/mem: Read Dynamic capacity configuration from the device

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Date:   Thu, 7 Sep 2023 08:46:04 -0700
From:   Alison Schofield <alison.schofield@...el.com>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Navneet Singh <navneet.singh@...el.com>,
        Fan Ni <fan.ni@...sung.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 03/18] cxl/mem: Read Dynamic capacity
 configuration from the device

On Mon, Aug 28, 2023 at 10:20:54PM -0700, Ira Weiny wrote:
> From: Navneet Singh <navneet.singh@...el.com>
> 
> Devices can optionally support Dynamic Capacity (DC).  These devices are
> known as Dynamic Capacity Devices (DCD).

snip

> 
> +static enum cxl_region_mode
> +cxl_decoder_to_region_mode(enum cxl_decoder_mode mode)
> +{
> +	switch (mode) {
> +	case CXL_DECODER_NONE:
> +		return CXL_REGION_NONE;
> +	case CXL_DECODER_RAM:
> +		return CXL_REGION_RAM;
> +	case CXL_DECODER_PMEM:
> +		return CXL_REGION_PMEM;
> +	case CXL_DECODER_DEAD:
> +		return CXL_REGION_DEAD;
> +	case CXL_DECODER_MIXED:
> +	default:
> +		return CXL_REGION_MIXED;
> +	}
> +
> +	return CXL_REGION_MIXED;

Can the paths to return _MIXED be simplified here?


> +}
> +
snip

> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index cd4a9ffdacc7..ed282dcd5cf5 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -374,6 +374,28 @@ static inline const char *cxl_decoder_mode_name(enum cxl_decoder_mode mode)
>  	return "mixed";
>  }
>  
> +enum cxl_region_mode {
> +	CXL_REGION_NONE,
> +	CXL_REGION_RAM,
> +	CXL_REGION_PMEM,
> +	CXL_REGION_MIXED,
> +	CXL_REGION_DEAD,
> +};

I'm concerned about _DEAD.
At first I was going to say name these as CXL_REGION_MODE_*, but it's
pretty obvious that these are mode words...except for DEAD. Is that 
an actual mode or is it some type of status? I don't think I see it
used yet.

> +
> +static inline const char *cxl_region_mode_name(enum cxl_region_mode mode)
> +{
> +	static const char * const names[] = {
> +		[CXL_REGION_NONE] = "none",
> +		[CXL_REGION_RAM] = "ram",
> +		[CXL_REGION_PMEM] = "pmem",
> +		[CXL_REGION_MIXED] = "mixed",
> +	};
> +
> +	if (mode >= CXL_REGION_NONE && mode <= CXL_REGION_MIXED)
> +		return names[mode];
> +	return "mixed";
> +}

snip

> +
>  /**
>   * struct cxl_memdev_state - Generic Type-3 Memory Device Class driver data
>   *
> @@ -449,6 +464,8 @@ struct cxl_dev_state {
>   * @enabled_cmds: Hardware commands found enabled in CEL.
>   * @exclusive_cmds: Commands that are kernel-internal only
>   * @total_bytes: sum of all possible capacities
> + * @static_cap: Sum of RAM and PMEM capacities
> + * @dynamic_cap: Complete DPA range occupied by DC regions

Wondering about renaming RAM and PMEM caps as 'static'.
They are changeable via set partition commands.


>   * @volatile_only_bytes: hard volatile capacity
>   * @persistent_only_bytes: hard persistent capacity
>   * @partition_align_bytes: alignment size for partition-able capacity
> @@ -456,6 +473,10 @@ struct cxl_dev_state {
>   * @active_persistent_bytes: sum of hard + soft persistent
>   * @next_volatile_bytes: volatile capacity change pending device reset
>   * @next_persistent_bytes: persistent capacity change pending device reset
> + * @nr_dc_region: number of DC regions implemented in the memory device
> + * @dc_region: array containing info about the DC regions
> + * @dc_event_log_size: The number of events the device can store in the
> + * Dynamic Capacity Event Log before it overflows
>   * @event: event log driver state
>   * @poison: poison driver state info
>   * @fw: firmware upload / activation state
> @@ -473,7 +494,10 @@ struct cxl_memdev_state {
>  	DECLARE_BITMAP(dcd_cmds, CXL_DCD_ENABLED_MAX);
>  	DECLARE_BITMAP(enabled_cmds, CXL_MEM_COMMAND_ID_MAX);
>  	DECLARE_BITMAP(exclusive_cmds, CXL_MEM_COMMAND_ID_MAX);
> +
>  	u64 total_bytes;
> +	u64 static_cap;
> +	u64 dynamic_cap;
>  	u64 volatile_only_bytes;
>  	u64 persistent_only_bytes;
>  	u64 partition_align_bytes;
> @@ -481,6 +505,11 @@ struct cxl_memdev_state {
>  	u64 active_persistent_bytes;
>  	u64 next_volatile_bytes;
>  	u64 next_persistent_bytes;
> +
> +	u8 nr_dc_region;
> +	struct cxl_dc_region_info dc_region[CXL_MAX_DC_REGION];
> +	size_t dc_event_log_size;
> +
>  	struct cxl_event_state event;
>  	struct cxl_poison_state poison;
>  	struct cxl_security_state security;
> @@ -587,6 +616,7 @@ struct cxl_mbox_identify {
>  	__le16 inject_poison_limit;
>  	u8 poison_caps;
>  	u8 qos_telemetry_caps;
> +	__le16 dc_event_log_size;
>  } __packed;
>  

snip

>  /*