Re: [PATCH v9 1/1] drm/xe: Add helper macro to loop each dss

["Dong, Zhanjun" <zhanjun.dong@intel.com>]

See my inline comments below.

Regards,
Zhanjun

On 2024-02-15 2:20 p.m., Michal Wajdeczko wrote:
> Hi Zhanjun,
> 
> I was about to push this patch, but it needs new revision, see below.
> Also added some nits
> 
> On 09.02.2024 18:45, Zhanjun Dong wrote:
>> Add helper macro to loop each dss. This is a precursor patch to allow
>> for easier iteration through MCR registers and other per-DSS uses.
> 
> nit: please be consistent on naming dss vs DSS
> 
>>
>> Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_gt_mcr.c      | 32 ++++++++++++++++++++++++++++-
>>   drivers/gpu/drm/xe/xe_gt_mcr.h      | 13 ++++++++++++
>>   drivers/gpu/drm/xe/xe_gt_topology.c | 31 +++++++++++++++++++++++++---
>>   drivers/gpu/drm/xe/xe_gt_topology.h |  1 +
>>   drivers/gpu/drm/xe/xe_gt_types.h    |  2 ++
>>   5 files changed, 75 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_gt_mcr.c b/drivers/gpu/drm/xe/xe_gt_mcr.c
>> index 8546cd3cc50d..44163fe8c7b9 100644
>> --- a/drivers/gpu/drm/xe/xe_gt_mcr.c
>> +++ b/drivers/gpu/drm/xe/xe_gt_mcr.c
>> @@ -6,6 +6,7 @@
>>   #include "xe_gt_mcr.h"
>>   
>>   #include "regs/xe_gt_regs.h"
>> +#include "xe_assert.h"
>>   #include "xe_gt.h"
>>   #include "xe_gt_topology.h"
>>   #include "xe_gt_types.h"
>> @@ -291,11 +292,40 @@ static void init_steering_mslice(struct xe_gt *gt)
>>   	gt->steering[LNCF].instance_target = 0;		/* unused */
>>   }
>>   
>> +static int get_dss_per_group(struct xe_gt *gt)
> 
> nit: shouldn't this function be 'unsigned int' ?
Sure, we can

> 
>> +{
>> +	return gt_to_xe(gt)->info.platform == XE_PVC ? 8 : 4;
>> +}
>> +
>> +/**
>> + * xe_gt_mcr_get_dss_steering - returns the group/instance steering for a DSS
>> + * @gt: GT structure
>> + * @dss: DSS ID to obtain steering for
>> + * @group: pointer to storage for steering group ID
>> + * @instance: pointer to storage for steering instance ID
>> + *
>> + * Returns the steering IDs (via the @group and @instance parameters) that
>> + * correspond to a specific DSS ID.
> 
> nit: this is a 'bool' function so having a "Return:" section is desired
Sure.
> 
>> + */
>> +bool xe_gt_mcr_get_dss_steering(struct xe_gt *gt, unsigned int dss, unsigned int *group,
>> +				unsigned int *instance)
>> +{
>> +	int dss_per_grp;
> 
> nit: this could be one-liner:
Sure.
> 
> 	unsigned int dss_per_grp = get_dss_per_group(gt);
> 
>> +
>> +	xe_gt_assert(gt, dss < XE_MAX_DSS_FUSE_BITS);
>> +
>> +	dss_per_grp = get_dss_per_group(gt);
>> +
>> +	*group = dss / dss_per_grp;
>> +	*instance = dss % dss_per_grp;
>> +	return true;
>> +}
>> +
>>   static void init_steering_dss(struct xe_gt *gt)
>>   {
>>   	unsigned int dss = min(xe_dss_mask_group_ffs(gt->fuse_topo.g_dss_mask, 0, 0),
>>   			       xe_dss_mask_group_ffs(gt->fuse_topo.c_dss_mask, 0, 0));
>> -	unsigned int dss_per_grp = gt_to_xe(gt)->info.platform == XE_PVC ? 8 : 4;
>> +	unsigned int dss_per_grp = get_dss_per_group(gt);
>>   
>>   	gt->steering[DSS].group_target = dss / dss_per_grp;
>>   	gt->steering[DSS].instance_target = dss % dss_per_grp;
> 
> nit: this looks like a good candidate to use this new function
> xe_gt_mcr_get_dss_steering() to avoid code duplication
No, the pointer type is (unsigned int *) for group and instance of 
xe_gt_mcr_get_dss_steering, while here the steering[DSS].group and 
instance is u16. The pointed data type uint is to match data type being 
used in loop body, where we don't use u16 normally.

I know it looks similar, but type mismatch here.

> 
> 
>> diff --git a/drivers/gpu/drm/xe/xe_gt_mcr.h b/drivers/gpu/drm/xe/xe_gt_mcr.h
>> index 27ca1bc880a0..5b4e74da82a1 100644
>> --- a/drivers/gpu/drm/xe/xe_gt_mcr.h
>> +++ b/drivers/gpu/drm/xe/xe_gt_mcr.h
>> @@ -7,6 +7,7 @@
>>   #define _XE_GT_MCR_H_
>>   
>>   #include "regs/xe_reg_defs.h"
>> +#include "xe_gt_topology.h"
>>   
>>   struct drm_printer;
>>   struct xe_gt;
>> @@ -25,5 +26,17 @@ void xe_gt_mcr_multicast_write(struct xe_gt *gt, struct xe_reg_mcr mcr_reg,
>>   			       u32 value);
>>   
>>   void xe_gt_mcr_steering_dump(struct xe_gt *gt, struct drm_printer *p);
>> +bool xe_gt_mcr_get_dss_steering(struct xe_gt *gt, unsigned int dss, unsigned int *group,
>> +				unsigned int *instance);
>> +
>> +/*
>> + * Loop over each DSS and determine the group and instance IDs that
>> + * should be used to steer MCR accesses toward this DSS.
>> + */
> 
> shouldn't this be regular kernel-doc  >
>> +#define for_each_dss_steering(dss_, gt_, group_, instance_) \
>> +	for (dss_ = xe_gt_topology_get_next_dss(gt, 0); \
> 
> BUG: using outside "gt" instead of "gt_" parameter
> 
> also it looks that upstream BKM is to _not_ use underscore for param
> names as params shouldn't leak anyway)
Thanks for point out the bug. Will fix it in next rev.

> 
> 
>> +	     dss_ >= 0; \
>> +	     dss_ = xe_gt_topology_get_next_dss(gt, dss_ + 1)) \
> 
> ditto
> 
>> +		for_each_if(xe_gt_mcr_get_dss_steering(gt_, dss_, &(group_), &(instance_)))
> 
> btw, did you consider to split this macro into two:
> 
> xe_gt_topology.h:
> 
> 	#define for_each_dss(dss, gt) \
> 		for (dss = xe_gt_topology_get_next_dss(gt, 0); \
> 		     dss >= 0; \
> 		     dss = xe_gt_topology_get_next_dss(gt, dss + 1))
> 
> xe_gt_mcr.h:
> 
> 	#define for_each_dss_steering(dss, gt, group, instance) \
> 		 for_each_if(xe_gt_mcr_get_dss_steering(gt, dss, &(group), &(instance)))
> 
We can split it if Jose need it.

>>   
>>   #endif /* _XE_GT_MCR_H_ */
>> diff --git a/drivers/gpu/drm/xe/xe_gt_topology.c b/drivers/gpu/drm/xe/xe_gt_topology.c
>> index a8d7f272c30a..97c0a4b8fe40 100644
>> --- a/drivers/gpu/drm/xe/xe_gt_topology.c
>> +++ b/drivers/gpu/drm/xe/xe_gt_topology.c
>> @@ -11,9 +11,6 @@
>>   #include "xe_gt.h"
>>   #include "xe_mmio.h"
>>   
>> -#define XE_MAX_DSS_FUSE_BITS (32 * XE_MAX_DSS_FUSE_REGS)
>> -#define XE_MAX_EU_FUSE_BITS (32 * XE_MAX_EU_FUSE_REGS)
>> -
>>   static void
>>   load_dss_mask(struct xe_gt *gt, xe_dss_mask_t mask, int numregs, ...)
>>   {
>> @@ -167,3 +164,31 @@ bool xe_gt_topology_has_dss_in_quadrant(struct xe_gt *gt, int quad)
>>   
>>   	return quad_first < (quad + 1) * dss_per_quad;
>>   }
>> +
>> +/**
>> + * xe_gt_topology_get_next_dss - returns the next DSS id from a start position
>> + * @gt: GT structure
>> + * @from: An index to start search form
> 
> typo s/form/from
Thanks
> 
>> + *
>> + * Search from this GT's DSS-fuses-topology and return the DSS-ID of the
>> + * next valid DSS instance after DSS-ID 'from'. Depending on the platform
>> + * construction, DSS instances could be for geometry (RENDER engine) or
>> + * compute (COMPUTE engine). However, all current platforms that have
>> + * both engines have the same instances thus we can combine both masks
>> + * internally before performing this operation.
>> + *
>> + * Return -1 if not found since given "from" position.
> 
> you should use "Return:" tag and likely say what is returned if found
Sure, will fix it.

> 
>> + */
>> +int xe_gt_topology_get_next_dss(struct xe_gt *gt, int from)
>> +{
>> +	xe_dss_mask_t all_dss;
>> +	unsigned long next;
>> +
>> +	bitmap_or(all_dss, gt->fuse_topo.g_dss_mask, gt->fuse_topo.c_dss_mask,
>> +		  XE_MAX_DSS_FUSE_BITS);
>> +
>> +	next = find_next_bit(all_dss, XE_MAX_DSS_FUSE_BITS, from);
>> +	if (next == XE_MAX_DSS_FUSE_BITS)
>> +		return -1;
>> +	return next;
>> +}
>> diff --git a/drivers/gpu/drm/xe/xe_gt_topology.h b/drivers/gpu/drm/xe/xe_gt_topology.h
>> index d1b54fb52ea6..44bd8a58f9ce 100644
>> --- a/drivers/gpu/drm/xe/xe_gt_topology.h
>> +++ b/drivers/gpu/drm/xe/xe_gt_topology.h
>> @@ -21,5 +21,6 @@ bool xe_dss_mask_empty(const xe_dss_mask_t mask);
>>   
>>   bool
>>   xe_gt_topology_has_dss_in_quadrant(struct xe_gt *gt, int quad);
>> +int xe_gt_topology_get_next_dss(struct xe_gt *gt, int from);
>>   
>>   #endif /* _XE_GT_TOPOLOGY_H_ */
>> diff --git a/drivers/gpu/drm/xe/xe_gt_types.h b/drivers/gpu/drm/xe/xe_gt_types.h
>> index 70c615dd1498..b926606edb38 100644
>> --- a/drivers/gpu/drm/xe/xe_gt_types.h
>> +++ b/drivers/gpu/drm/xe/xe_gt_types.h
>> @@ -25,7 +25,9 @@ enum xe_gt_type {
>>   };
>>   
>>   #define XE_MAX_DSS_FUSE_REGS	3
>> +#define XE_MAX_DSS_FUSE_BITS	(32 * XE_MAX_DSS_FUSE_REGS)
>>   #define XE_MAX_EU_FUSE_REGS	1
>> +#define XE_MAX_EU_FUSE_BITS	(32 * XE_MAX_EU_FUSE_REGS)
>>   
>>   typedef unsigned long xe_dss_mask_t[BITS_TO_LONGS(32 * XE_MAX_DSS_FUSE_REGS)];
>>   typedef unsigned long xe_eu_mask_t[BITS_TO_LONGS(32 * XE_MAX_EU_FUSE_REGS)];
> 
> nit: above looks like a good candidates to use new FUSE_BITS definitions
Sure, will do it that way.
> 
> Michal
>