[2/3] firmware: arm_scmi: Fix freq/power truncation in the perf protocol

  Fix frequency and power truncation seen in the performance protocol by
casting it with the correct type.

Fixes: a9e3fbfaa0ff ("firmware: arm_scmi: add initial support for performance protocol")
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
---
 drivers/firmware/arm_scmi/perf.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)
  

On Wed, Nov 29, 2023 at 12:27:47PM +0530, Sibi Sankar wrote:
> Fix frequency and power truncation seen in the performance protocol by
> casting it with the correct type.
>

While I always remembered to handle this when reviewing the spec, seem to
have forgotten when it came to handling in the implementation :(. Thanks
for spotting this.

However I don't like the ugly type casting. I think we can do better. Also
looking at the code around the recently added level index mode, I think we
can simplify things like below patch.

Cristian,
What do you think ?

Regards,
Sudeep

-->8

 drivers/firmware/arm_scmi/perf.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
index a648521e04a3..2e828b29efab 100644
--- a/drivers/firmware/arm_scmi/perf.c
+++ b/drivers/firmware/arm_scmi/perf.c
@@ -268,13 +268,14 @@ scmi_perf_domain_attributes_get(const struct scmi_protocol_handle *ph,
 		dom_info->sustained_perf_level =
 					le32_to_cpu(attr->sustained_perf_level);
 		if (!dom_info->sustained_freq_khz ||
-		    !dom_info->sustained_perf_level)
+		    !dom_info->sustained_perf_level ||
+		    dom_info->level_indexing_mode)
 			/* CPUFreq converts to kHz, hence default 1000 */
 			dom_info->mult_factor =	1000;
 		else
 			dom_info->mult_factor =
-					(dom_info->sustained_freq_khz * 1000) /
-					dom_info->sustained_perf_level;
+					(dom_info->sustained_freq_khz * 1000UL)
+					/ dom_info->sustained_perf_level;
 		strscpy(dom_info->info.name, attr->name,
 			SCMI_SHORT_NAME_MAX_SIZE);
 	}
@@ -804,9 +805,10 @@ static int scmi_dvfs_device_opps_add(const struct scmi_protocol_handle *ph,

 	for (idx = 0; idx < dom->opp_count; idx++) {
 		if (!dom->level_indexing_mode)
-			freq = dom->opp[idx].perf * dom->mult_factor;
+			freq = dom->opp[idx].perf;
 		else
-			freq = dom->opp[idx].indicative_freq * 1000;
+			freq = dom->opp[idx].indicative_freq;
+		freq *= dom->mult_factor;

 		data.level = dom->opp[idx].perf;
 		data.freq = freq;
@@ -879,7 +881,7 @@ static int scmi_dvfs_freq_get(const struct scmi_protocol_handle *ph, u32 domain,
 		return ret;

 	if (!dom->level_indexing_mode) {
-		*freq = level * dom->mult_factor;
+		*freq = level;
 	} else {
 		struct scmi_opp *opp;

@@ -887,8 +889,9 @@ static int scmi_dvfs_freq_get(const struct scmi_protocol_handle *ph, u32 domain,
 		if (!opp)
 			return -EIO;

-		*freq = opp->indicative_freq * 1000;
+		*freq = opp->indicative_freq;
 	}
+	freq *= dom->mult_factor;

 	return ret;
 }
@@ -908,9 +911,10 @@ static int scmi_dvfs_est_power_get(const struct scmi_protocol_handle *ph,

 	for (opp = dom->opp, idx = 0; idx < dom->opp_count; idx++, opp++) {
 		if (!dom->level_indexing_mode)
-			opp_freq = opp->perf * dom->mult_factor;
+			opp_freq = opp->perf;
 		else
-			opp_freq = opp->indicative_freq * 1000;
+			opp_freq = opp->indicative_freq;
+		opp_freq *= dom->mult_factor;

 		if (opp_freq < *freq)
 			continue;
  

On Thu, Nov 30, 2023 at 12:49:42PM +0000, Cristian Marussi wrote:
> On Thu, Nov 30, 2023 at 12:05:06PM +0000, Sudeep Holla wrote:
> > On Wed, Nov 29, 2023 at 12:27:47PM +0530, Sibi Sankar wrote:
> > > Fix frequency and power truncation seen in the performance protocol by
> > > casting it with the correct type.
> > >
> > 
> > While I always remembered to handle this when reviewing the spec, seem to
> > have forgotten when it came to handling in the implementation :(. Thanks
> > for spotting this.
> > 
> > However I don't like the ugly type casting. I think we can do better. Also
> > looking at the code around the recently added level index mode, I think we
> > can simplify things like below patch.
> > 
> > Cristian,
> > What do you think ?
> > 
> 
> Hi
> 
> the cleanup seems nice in general to compact the mult_factor multipliers
> in one place, and regarding addressing the problem of truncation without
> the need of the explicit casting, should not be enough to change to
> additionally also change mult_factor to be an u64 ?
>

I started exactly with that, but when I completed the patch, there was no
explicit need for it, so dropped it again. I can bump mult_factor to be
u64 but do you see any other place that would need it apart from having
single statement that does multiplication and assignment ? I am exploiting
the conditional based on level_indexing_mode here but I agree it may help
in backporting if I make mult_factor u64.
  

On Thu, Nov 30, 2023 at 01:56:56PM +0000, Sudeep Holla wrote:
> On Thu, Nov 30, 2023 at 12:49:42PM +0000, Cristian Marussi wrote:
> > On Thu, Nov 30, 2023 at 12:05:06PM +0000, Sudeep Holla wrote:
> > > On Wed, Nov 29, 2023 at 12:27:47PM +0530, Sibi Sankar wrote:
> > > > Fix frequency and power truncation seen in the performance protocol by
> > > > casting it with the correct type.
> > > >
> > > 
> > > While I always remembered to handle this when reviewing the spec, seem to
> > > have forgotten when it came to handling in the implementation :(. Thanks
> > > for spotting this.
> > > 
> > > However I don't like the ugly type casting. I think we can do better. Also
> > > looking at the code around the recently added level index mode, I think we
> > > can simplify things like below patch.
> > > 
> > > Cristian,
> > > What do you think ?
> > > 
> > 
> > Hi
> > 
> > the cleanup seems nice in general to compact the mult_factor multipliers
> > in one place, and regarding addressing the problem of truncation without
> > the need of the explicit casting, should not be enough to change to
> > additionally also change mult_factor to be an u64 ?
> >
> 
> I started exactly with that, but when I completed the patch, there was no
> explicit need for it, so dropped it again. I can bump mult_factor to be
> u64 but do you see any other place that would need it apart from having
> single statement that does multiplication and assignment ? I am exploiting
> the conditional based on level_indexing_mode here but I agree it may help
> in backporting if I make mult_factor u64.
> 

Ah right

   freq *= dom->multi_fact;

does the trick..but cannot this by itself (under unplausibl conds)
overflow and does not fit into a u32 mult_factor ?

 dom_info->mult_factor =
 	(dom_info->sustained_freq_khz * 1000UL)
	/ dom_info->sustained_perf_level;


Thanks,
Cristian
  

On 11/30/23 21:55, Cristian Marussi wrote:
> On Thu, Nov 30, 2023 at 01:56:56PM +0000, Sudeep Holla wrote:
>> On Thu, Nov 30, 2023 at 12:49:42PM +0000, Cristian Marussi wrote:
>>> On Thu, Nov 30, 2023 at 12:05:06PM +0000, Sudeep Holla wrote:
>>>> On Wed, Nov 29, 2023 at 12:27:47PM +0530, Sibi Sankar wrote:
>>>>> Fix frequency and power truncation seen in the performance protocol by
>>>>> casting it with the correct type.
>>>>>
>>>>
>>>> While I always remembered to handle this when reviewing the spec, seem to
>>>> have forgotten when it came to handling in the implementation :(. Thanks
>>>> for spotting this.
>>>>
>>>> However I don't like the ugly type casting. I think we can do better. Also
>>>> looking at the code around the recently added level index mode, I think we
>>>> can simplify things like below patch.
>>>>
>>>> Cristian,
>>>> What do you think ?
>>>>
>>>
>>> Hi
>>>
>>> the cleanup seems nice in general to compact the mult_factor multipliers
>>> in one place, and regarding addressing the problem of truncation without
>>> the need of the explicit casting, should not be enough to change to
>>> additionally also change mult_factor to be an u64 ?
>>>
>>
>> I started exactly with that, but when I completed the patch, there was no
>> explicit need for it, so dropped it again. I can bump mult_factor to be
>> u64 but do you see any other place that would need it apart from having
>> single statement that does multiplication and assignment ? I am exploiting
>> the conditional based on level_indexing_mode here but I agree it may help
>> in backporting if I make mult_factor u64.
>>
> 
> Ah right
> 
>     freq *= dom->multi_fact;
> 
> does the trick..but cannot this by itself (under unplausibl conds)
> overflow and does not fit into a u32 mult_factor ?
> 
>   dom_info->mult_factor =
>   	(dom_info->sustained_freq_khz * 1000UL)

wouldn't having the 1000UL ensure that we don't truncate though?
Anyway will drop the patch when I re-spin the series.

-Sibi

> 	/ dom_info->sustained_perf_level;
> 
> 
> Thanks,
> Cristian
>
  

On Thu, Nov 30, 2023 at 04:25:44PM +0000, Cristian Marussi wrote:
> On Thu, Nov 30, 2023 at 01:56:56PM +0000, Sudeep Holla wrote:
> > I started exactly with that, but when I completed the patch, there was no
> > explicit need for it, so dropped it again. I can bump mult_factor to be
> > u64 but do you see any other place that would need it apart from having
> > single statement that does multiplication and assignment ? I am exploiting
> > the conditional based on level_indexing_mode here but I agree it may help
> > in backporting if I make mult_factor u64.
> > 
> 
> Ah right
> 
>    freq *= dom->multi_fact;
> 
> does the trick..but cannot this by itself (under unplausibl conds)
> overflow and does not fit into a u32 mult_factor ?
> 
>  dom_info->mult_factor =
>  	(dom_info->sustained_freq_khz * 1000UL)
> 	/ dom_info->sustained_perf_level;

Agreed. Also thinking about backports, I think making it u64 is simple
fix. I will also thinking of splitting the changes so that fixes are
more appropriate. I will try to post something soonish.

--
Regards,
Sudeep
  

On Fri, Dec 01, 2023 at 01:02:25AM +0530, Sibi Sankar wrote:
>
> On 11/30/23 21:55, Cristian Marussi wrote:
> >
> > Ah right
> >
> >     freq *= dom->multi_fact;
> >
> > does the trick..but cannot this by itself (under unplausibl conds)
> > overflow and does not fit into a u32 mult_factor ?
> >
> >   dom_info->mult_factor =
> >   	(dom_info->sustained_freq_khz * 1000UL)
>
> wouldn't having the 1000UL ensure that we don't truncate though?

Correct but the point was mult_factor itself can be >= 2^32

> Anyway will drop the patch when I re-spin the series.
>

Are you re-spining just to change 24 to 32 in PATCH 3/3, if so no need.
I have already applied 1 and 3 here[1]. Just waiting for the builder
results to confirm it

--
Regards,
Sudeep

[1] https://git.kernel.org/pub/scm/linux/kernel/git/sudeep.holla/linux.git/log/?h=for-next/scmi/updates