Re: [PATCH v2 09/14] drm/dp-mst: Export symbols for dpcd read/write

["Li, Sun peng (Leo)" <Sunpeng.Li-5C7GfCeVMHo@public.gmane.org>]

On 2019-08-20 5:02 p.m., Lyude Paul wrote:
> [Added Leo Li here, since they did the auxdev work that introduced these
> functions]
> 
> Since it seems we'll actually be doing remote DPCD read/writes in DRM drivers
> and not just from auxdev, maybe we should combine drm_dp_dpcd_read() with
> drm_dp_mst_dpcd_read() and do the same with the _write() variants? Based on
> previous discussions with Leo Li I remember that we can't just combine the
> dp_aux_dev->transfer() callbacks in struct drm_dp_aux_dev, but I don't see a
> reason we can't just teach drm_dp_dpcd_read/write() to work with MST aux so
> that we don't need two seperate functions. This should be pretty easy to do,
> just:
> 
> /* Add a check like this at the start of drm_dp_dpcd_read(): */
> ssize_t drm_dp_dpcd_read(...) {
> 	if (aux->is_remote)
> 		return drm_dp_mst_dpcd_read(...);
> 
> 	/* ... */
> }
> 
> /* And in drm_dp_dpcd_write(): */
> ssize_t drm_dp_dpcd_write(...) {
> 	if (aux->is_remote)
> 		return drm_dp_mst_dpcd_write(...);
> 
> 	/* ... */
> }
> 
> Then just replace the manual calls to drm_dp_mst_dpcd_write() in
> drivers/gpu/drm/drm_dp_aux_dev.c with normal
> drm_dp_dpcd_read()/drm_dp_dpcd_write() calls. Thoughts?

I think this would work well.

drm_dp_mst_dpcd_read/write will eventually call drm_dp_dpcd_write, so
doing so would cause a recursive call. That should be safe though. The
mst manager's aux will be used, and that should always be a real
(is_remote == false) aux, fwict.

Essentially, it's just moving that conditional from
auxdev_read/write_iter to drm_dp_dpcd_read/write.

Leo

> 
> On Tue, 2019-08-20 at 15:11 -0400, David Francis wrote:
>> To use these functions in drm driver directories, they must be
>> exported
>>
>> Signed-off-by: David Francis <David.Francis@amd.com>
>> ---
>>  drivers/gpu/drm/drm_dp_mst_topology.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
>> b/drivers/gpu/drm/drm_dp_mst_topology.c
>> index b40d975aec76..5d5bd42da17c 100644
>> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
>> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>> @@ -1512,6 +1512,7 @@ ssize_t drm_dp_mst_dpcd_read(struct drm_dp_aux *aux,
>>  	return drm_dp_send_dpcd_read(port->mgr, port,
>>  				     offset, size, buffer);
>>  }
>> +EXPORT_SYMBOL(drm_dp_mst_dpcd_read);
>>  
>>  /**
>>   * drm_dp_mst_dpcd_write() - write a series of bytes to the DPCD via
>> sideband
>> @@ -1535,6 +1536,7 @@ ssize_t drm_dp_mst_dpcd_write(struct drm_dp_aux *aux,
>>  	return drm_dp_send_dpcd_write(port->mgr, port,
>>  				      offset, size, buffer);
>>  }
>> +EXPORT_SYMBOL(drm_dp_mst_dpcd_write);
>>  
>>  static void drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, u8
>> *guid)
>>  {
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