Subject: Re: [PATCH 2/3] powerpc/pseries: Little endian fixes for post mobility device tree update

From: Tyrel Datwyler <[email-masked]>
Date: Tue, 03 Mar 2015 15:15:30 -0800

On 03/02/2015 01:49 PM, Tyrel Datwyler wrote:
> On 03/01/2015 09:20 PM, Cyril Bur wrote:
>> On Fri, 2015-02-27 at 18:24 -0800, Tyrel Datwyler wrote:
>>> We currently use the device tree update code in the kernel after resuming
>>> from a suspend operation to re-sync the kernels view of the device tree with
>>> that of the hypervisor. The code as it stands is not endian safe as it relies
>>> on parsing buffers returned by RTAS calls that thusly contains data in big
>>> endian format.
>>>
>>> This patch annotates variables and structure members with __be types as well
>>> as performing necessary byte swaps to cpu endian for data that needs to be
>>> parsed.
>>>
>>> Signed-off-by: Tyrel Datwyler <[email-masked]>
>>> ---
>>>  arch/powerpc/platforms/pseries/mobility.c | 36 ++++++++++++++++---------------
>>>  1 file changed, 19 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
>>> index 29e4f04..0b1f70e 100644
>>> --- a/arch/powerpc/platforms/pseries/mobility.c
>>> +++ b/arch/powerpc/platforms/pseries/mobility.c
>>> @@ -25,10 +25,10 @@
>>>  static struct kobject *mobility_kobj;
>>>  
>>>  struct update_props_workarea {
>>> -	u32 phandle;
>>> -	u32 state;
>>> -	u64 reserved;
>>> -	u32 nprops;
>>> +	__be32 phandle;
>>> +	__be32 state;
>>> +	__be64 reserved;
>>> +	__be32 nprops;
>>>  } __packed;
>>>  
>>>  #define NODE_ACTION_MASK	0xff000000
>>> @@ -127,7 +127,7 @@ static int update_dt_property(struct device_node *dn, struct property **prop,
>>>  	return 0;
>>>  }
>>>  
>>> -static int update_dt_node(u32 phandle, s32 scope)
>>> +static int update_dt_node(__be32 phandle, s32 scope)
>>>  {
>>
>> On line 153 of this function:
>>    dn = of_find_node_by_phandle(phandle);
>>
>> You're passing a __be32 to device tree code, if we can treat the phandle
>> as a opaque value returned to us from the rtas call and pass it around
>> like that then all good.

After digging deeper the device_node->phandle is stored in cpu endian
under the covers. So, for the of_find_node_by_phandle() we do need to
convert the phandle to cpu endian first. It appears I got lucky with the
update fixing the observed RMC issue because the phandle for the root
node seems to always be 0xffffffff.

-Tyrel

> 
> Yes, of_find_node_by_phandle directly compares phandle passed in against
> the handle stored in each device_node when searching for a matching
> node. Since, the device tree is big endian it follows that the big
> endian phandle received in the rtas buffer needs no conversion.
> 
> Further, we need to pass the phandle to ibm,update-properties in the
> work area which is also required to be big endian. So, again it seemed
> that converting to cpu endian was a waste of effort just to convert it
> back to big endian.
> 
>> Its also hard to be sure if these need to be BE and have always been
>> that way because we've always run BE so they've never actually wanted
>> CPU endian its just that CPU endian has always been BE (I think I
>> started rambling...)
>>
>> Just want to check that *not* converting them is done on purpose.
> 
> Yes, I explicitly did not convert them on purpose. As mentioned above we
> need phandle in BE for the ibm,update-properties rtas work area.
> Similarly, drc_index needs to be in BE for the ibm,configure-connector
> rtas work area. Outside, of that we do no other manipulation of those
> values.
> 
>>
>> And having read on, I'm assuming the answer is yes since this
>> observation is true for your changes which affect:
>> 	delete_dt_node()
>> 	update_dt_node()
>>         add_dt_node()
>> Worth noting that you didn't change the definition of delete_dt_node()
> 
> You are correct. Oversight. I will fix that as it should generate a
> sparse complaint.
> 
> -Tyrel
> 
>>
>> I'll have a look once you address the non compiling in patch 1/3 (I'm
>> getting blocked the unused var because somehow Werror is on, odd it
>> didn't trip you up) but I also suspect this will have sparse go a bit
>> nuts. 
>> I wonder if there is a nice way of shutting sparse up.
>>
>>>  	struct update_props_workarea *upwa;
>>>  	struct device_node *dn;
>>> @@ -136,6 +136,7 @@ static int update_dt_node(u32 phandle, s32 scope)
>>>  	char *prop_data;
>>>  	char *rtas_buf;
>>>  	int update_properties_token;
>>> +	u32 nprops;
>>>  	u32 vd;
>>>  
>>>  	update_properties_token = rtas_token("ibm,update-properties");
>>> @@ -162,6 +163,7 @@ static int update_dt_node(u32 phandle, s32 scope)
>>>  			break;
>>>  
>>>  		prop_data = rtas_buf + sizeof(*upwa);
>>> +		nprops = be32_to_cpu(upwa->nprops);
>>>  
>>>  		/* On the first call to ibm,update-properties for a node the
>>>  		 * the first property value descriptor contains an empty
>>> @@ -170,17 +172,17 @@ static int update_dt_node(u32 phandle, s32 scope)
>>>  		 */
>>>  		if (*prop_data == 0) {
>>>  			prop_data++;
>>> -			vd = *(u32 *)prop_data;
>>> +			vd = be32_to_cpu(*(__be32 *)prop_data);
>>>  			prop_data += vd + sizeof(vd);
>>> -			upwa->nprops--;
>>> +			nprops--;
>>>  		}
>>>  
>>> -		for (i = 0; i < upwa->nprops; i++) {
>>> +		for (i = 0; i < nprops; i++) {
>>>  			char *prop_name;
>>>  
>>>  			prop_name = prop_data;
>>>  			prop_data += strlen(prop_name) + 1;
>>> -			vd = *(u32 *)prop_data;
>>> +			vd = be32_to_cpu(*(__be32 *)prop_data);
>>>  			prop_data += sizeof(vd);
>>>  
>>>  			switch (vd) {
>>> @@ -212,7 +214,7 @@ static int update_dt_node(u32 phandle, s32 scope)
>>>  	return 0;
>>>  }
>>>  
>>> -static int add_dt_node(u32 parent_phandle, u32 drc_index)
>>> +static int add_dt_node(__be32 parent_phandle, __be32 drc_index)
>>>  {
>>>  	struct device_node *dn;
>>>  	struct device_node *parent_dn;
>>> @@ -237,7 +239,7 @@ static int add_dt_node(u32 parent_phandle, u32 drc_index)
>>>  int pseries_devicetree_update(s32 scope)
>>>  {
>>>  	char *rtas_buf;
>>> -	u32 *data;
>>> +	__be32 *data;
>>>  	int update_nodes_token;
>>>  	int rc;
>>>  
>>> @@ -254,17 +256,17 @@ int pseries_devicetree_update(s32 scope)
>>>  		if (rc && rc != 1)
>>>  			break;
>>>  
>>> -		data = (u32 *)rtas_buf + 4;
>>> -		while (*data & NODE_ACTION_MASK) {
>>> +		data = (__be32 *)rtas_buf + 4;
>>> +		while (be32_to_cpu(*data) & NODE_ACTION_MASK) {
>>>  			int i;
>>> -			u32 action = *data & NODE_ACTION_MASK;
>>> -			int node_count = *data & NODE_COUNT_MASK;
>>> +			u32 action = be32_to_cpu(*data) & NODE_ACTION_MASK;
>>> +			u32 node_count = be32_to_cpu(*data) & NODE_COUNT_MASK;
>>>  
>>>  			data++;
>>>  
>>>  			for (i = 0; i < node_count; i++) {
>>> -				u32 phandle = *data++;
>>> -				u32 drc_index;
>>> +				__be32 phandle = *data++;
>>> +				__be32 drc_index;
>>>  
>>>  				switch (action) {
>>>  				case DELETE_DT_NODE:
>>
>> The patch looks good, no nonsense endian fixing. 
>> Worth noting that it leaves existing bugs in place, which is fine, I'll
>> rebase my patches which address endian and bugs on top of these so as to
>> address the bugs.
>>
>>
> 
> _______________________________________________
> Linuxppc-dev mailing list
> [email-masked]
> https://lists.ozlabs.org/listinfo/linuxppc-dev
>