Re: [PATCH 2/2] drm/xe/guc: Add support for NPK as a GuC log target

[John Harrison <john.c.harrison@intel.com>]

On 6/11/2025 3:04 PM, Cavitt, Jonathan wrote:
> -----Original Message-----
> From: Intel-xe <intel-xe-bounces@lists.freedesktop.org> On Behalf Of John.C.Harrison@Intel.com
> Sent: Wednesday, June 11, 2025 2:06 PM
> To: Intel-Xe@Lists.FreeDesktop.Org
> Cc: Harrison, John C <john.c.harrison@intel.com>
> Subject: [PATCH 2/2] drm/xe/guc: Add support for NPK as a GuC log target
>> From: John Harrison <John.C.Harrison@Intel.com>
>>
>> The GuC has an option to write log data via NPK. This is basically a
>> magic IO address that GuC writes arbitrary data to and which can be
>> logged by a suitable hardware logger. This can allow retrieval of the
>> GuC log in hardware debug environments even when the system as a whole
>> dies horribly.
>>
>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> So, this is basically a new modparam value that redirects GuC logs to
> a specific IO address?  I take it guc_log_target = 2 is the default value, and
> guc_log_target = 1 would print the logs to stdout, then?  I'd ask why we
> use 0 as a default value and not just default to 2 all the time, but I think I
> already know why (we need to guard against guc_log_target = 0 anyways
> to prevent printing to stdin).
Um, read the patch - "(0=memory [default], 1 = NPK, 2 = memory + NPK)". 
The default is zero. And no, nothing prints to stdout. This is about 
hardware level debugging. It has nothing to do with stdin/stdout/stderr. 
Those concepts do not exist in hardware nor in the KMD. If you send the 
GuC log to the NPK target then you need a hardware debugger (JTAG, etc.) 
to read it, as described in the commit message.

>
> I also take it this is modified on boot by, for example, writing
> "xe.guc_log_target=1" to CMDLINE_LINUX_DEFAULT as a part of the grub file.
That is generally how module parameters work. You can also set via 
modprobe.conf files as long as the Xe driver is a module and not 
compiled in.

John.

>
> Yeah, seems good.
> Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> -Jonathan Cavitt
>
>> ---
>>   drivers/gpu/drm/xe/xe_guc.c    | 4 ++++
>>   drivers/gpu/drm/xe/xe_module.c | 4 ++++
>>   drivers/gpu/drm/xe/xe_module.h | 1 +
>>   3 files changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_guc.c b/drivers/gpu/drm/xe/xe_guc.c
>> index e16d19b44bcc..9c0e3113f7d5 100644
>> --- a/drivers/gpu/drm/xe/xe_guc.c
>> +++ b/drivers/gpu/drm/xe/xe_guc.c
>> @@ -35,6 +35,7 @@
>>   #include "xe_guc_submit.h"
>>   #include "xe_memirq.h"
>>   #include "xe_mmio.h"
>> +#include "xe_module.h"
>>   #include "xe_platform_types.h"
>>   #include "xe_sriov.h"
>>   #include "xe_uc.h"
>> @@ -74,6 +75,9 @@ static u32 guc_ctl_debug_flags(struct xe_guc *guc)
>>   	else
>>   		flags |= FIELD_PREP(GUC_LOG_VERBOSITY, GUC_LOG_LEVEL_TO_VERBOSITY(level));
>>   
>> +	if (xe_modparam.guc_log_target)
>> +		flags |= FIELD_PREP(GUC_LOG_DESTINATION, xe_modparam.guc_log_target);
>> +
>>   	return flags;
>>   }
>>   
>> diff --git a/drivers/gpu/drm/xe/xe_module.c b/drivers/gpu/drm/xe/xe_module.c
>> index 1c4dfafbcd0b..fc8c681819b9 100644
>> --- a/drivers/gpu/drm/xe/xe_module.c
>> +++ b/drivers/gpu/drm/xe/xe_module.c
>> @@ -21,6 +21,7 @@
>>   struct xe_modparam xe_modparam = {
>>   	.probe_display = true,
>>   	.guc_log_level = 3,
>> +	.guc_log_target = 0,
>>   	.force_probe = CONFIG_DRM_XE_FORCE_PROBE,
>>   #ifdef CONFIG_PCI_IOV
>>   	.max_vfs = IS_ENABLED(CONFIG_DRM_XE_DEBUG) ? ~0 : 0,
>> @@ -45,6 +46,9 @@ MODULE_PARM_DESC(vram_bar_size, "Set the vram bar size (in MiB) - <0=disable-res
>>   module_param_named(guc_log_level, xe_modparam.guc_log_level, int, 0600);
>>   MODULE_PARM_DESC(guc_log_level, "GuC firmware logging level (0=disable, 1..5=enable with verbosity min..max)");
>>   
>> +module_param_named(guc_log_target, xe_modparam.guc_log_target, int, 0600);
>> +MODULE_PARM_DESC(guc_log_target, "GuC firmware logging target (0=memory [default], 1 = NPK, 2 = memory + NPK)");
>> +
>>   module_param_named_unsafe(guc_firmware_path, xe_modparam.guc_firmware_path, charp, 0400);
>>   MODULE_PARM_DESC(guc_firmware_path,
>>   		 "GuC firmware path to use instead of the default one");
>> diff --git a/drivers/gpu/drm/xe/xe_module.h b/drivers/gpu/drm/xe/xe_module.h
>> index 5a3bfea8b7b4..4d978f6f26b6 100644
>> --- a/drivers/gpu/drm/xe/xe_module.h
>> +++ b/drivers/gpu/drm/xe/xe_module.h
>> @@ -14,6 +14,7 @@ struct xe_modparam {
>>   	bool probe_display;
>>   	u32 force_vram_bar_size;
>>   	int guc_log_level;
>> +	int guc_log_target;
>>   	char *guc_firmware_path;
>>   	char *huc_firmware_path;
>>   	char *gsc_firmware_path;
>> -- 
>> 2.49.0
>>
>>