[0/3] soundwire: use UniqueID only when relevant

Message

Pierre-Louis Bossart Oct. 22, 2019, 11:48 p.m. UTC

The hardware UniqueID, typically enabled with pin-strapping, is
required during enumeration to avoid conflicts between devices of the
same type.

When there are no devices of the same type, using the UniqueID is
overkill and results in a lot of probe errors due to mismatches
between ACPI tables and hardware capabilities. For example it's not
uncommon for BIOS vendors to copy/paste the same settings between
platforms but the hardware pin-strapping is different. This is
perfectly legit and permitted by MIPI specs.

With this patchset, the UniqueID is only used when multiple devices of
the same type are detected. The loop to detect multiple identical
devices is not super efficient but with typically fewer than 4 devices
per link there's no real incentive to be smarter.

This change is only implemented for ACPI platforms, for DeviceTree
there is no change.

Pierre-Louis Bossart (3):
  soundwire: remove bitfield for unique_id, use u8
  soundwire: slave: add helper to extract slave ID
  soundwire: ignore uniqueID when irrelevant

 drivers/soundwire/bus.c       |  7 +--
 drivers/soundwire/slave.c     | 98 +++++++++++++++++++++++++++--------
 include/linux/soundwire/sdw.h |  4 +-
 3 files changed, 84 insertions(+), 25 deletions(-)

Comments

Pierre-Louis Bossart Nov. 6, 2019, 7:30 p.m. UTC | #1

On 10/22/19 6:48 PM, Pierre-Louis Bossart wrote:
> The hardware UniqueID, typically enabled with pin-strapping, is
> required during enumeration to avoid conflicts between devices of the
> same type.
> 
> When there are no devices of the same type, using the UniqueID is
> overkill and results in a lot of probe errors due to mismatches
> between ACPI tables and hardware capabilities. For example it's not
> uncommon for BIOS vendors to copy/paste the same settings between
> platforms but the hardware pin-strapping is different. This is
> perfectly legit and permitted by MIPI specs.
> 
> With this patchset, the UniqueID is only used when multiple devices of
> the same type are detected. The loop to detect multiple identical
> devices is not super efficient but with typically fewer than 4 devices
> per link there's no real incentive to be smarter.
> 
> This change is only implemented for ACPI platforms, for DeviceTree
> there is no change.

Vinod, this series has been submitted for review on October 22 and I 
answered to your questions. There's been no feedback since October 24, 
so is there any sustained objection here?

ACPI platforms are completely unmanageable without this patchset.

> 
> Pierre-Louis Bossart (3):
>    soundwire: remove bitfield for unique_id, use u8
>    soundwire: slave: add helper to extract slave ID
>    soundwire: ignore uniqueID when irrelevant
> 
>   drivers/soundwire/bus.c       |  7 +--
>   drivers/soundwire/slave.c     | 98 +++++++++++++++++++++++++++--------
>   include/linux/soundwire/sdw.h |  4 +-
>   3 files changed, 84 insertions(+), 25 deletions(-)
>

Vinod Koul Nov. 9, 2019, 11:18 a.m. UTC | #2

On 22-10-19, 18:48, Pierre-Louis Bossart wrote:
> The hardware UniqueID, typically enabled with pin-strapping, is
> required during enumeration to avoid conflicts between devices of the
> same type.
> 
> When there are no devices of the same type, using the UniqueID is
> overkill and results in a lot of probe errors due to mismatches
> between ACPI tables and hardware capabilities. For example it's not
> uncommon for BIOS vendors to copy/paste the same settings between
> platforms but the hardware pin-strapping is different. This is
> perfectly legit and permitted by MIPI specs.
> 
> With this patchset, the UniqueID is only used when multiple devices of
> the same type are detected. The loop to detect multiple identical
> devices is not super efficient but with typically fewer than 4 devices
> per link there's no real incentive to be smarter.
> 
> This change is only implemented for ACPI platforms, for DeviceTree
> there is no change.

I do not fully agree with the approach here but I do understand why this
was done and do not have a better alternative, so applied now