On 16.09.2019 14:02, Brian Masney wrote:

On Mon, Sep 16, 2019 at 01:32:58PM +0200, Enric Balletbo i Serra wrote:

quoted

Hi,

On 16/9/19 12:49, Laurent Pinchart wrote:

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Hi Brian,

On Mon, Sep 16, 2019 at 06:36:14AM -0400, Brian Masney wrote:

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On Mon, Sep 16, 2019 at 12:02:09PM +0200, Andrzej Hajda wrote:

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On 15.08.2019 02:48, Brian Masney wrote:

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When attempting to configure this driver on a Nexus 5 phone (msm8974),
setting up the dummy i2c bus for TX_P0 would fail due to an -EBUSY
error. The downstream MSM kernel sources [1] shows that the proper value
for TX_P0 is 0x78, not 0x70, so correct the value to allow device
probing to succeed.

[1] https://github.com/AICP/kernel_lge_hammerhead/blob/n7.1/drivers/video/slimport/slimport_tx_reg.h

Signed-off-by: Brian Masney <redacted>
---
 drivers/gpu/drm/bridge/analogix-anx78xx.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/analogix-anx78xx.h b/drivers/gpu/drm/bridge/analogix-anx78xx.h
index 25e063bcecbc..bc511fc605c9 100644
--- a/drivers/gpu/drm/bridge/analogix-anx78xx.h
+++ b/drivers/gpu/drm/bridge/analogix-anx78xx.h

@@ -6,7 +6,7 @@
 #ifndef __ANX78xx_H
 #define __ANX78xx_H
 
-#define TX_P0				0x70
+#define TX_P0				0x78

This bothers me little. There are no upstream users, grepping android
sources suggests that both values can be used [1][2]  (grep for "#define
TX_P0"), moreover there is code suggesting both values can be valid [3].

Could you verify datasheet which i2c slave addresses are valid for this
chip, if both I guess this patch should be reworked.


[1]:
https://android.googlesource.com/kernel/msm/+/android-msm-flo-3.4-jb-mr2/drivers/misc/slimport_anx7808/slimport_tx_reg.h

[2]:
https://github.com/AndroidGX/SimpleGX-MM-6.0_H815_20d/blob/master/drivers/video/slimport/anx7812/slimport7812_tx_reg.h

[3]:
https://github.com/commaai/android_kernel_leeco_msm8996/blob/master/drivers/video/msm/mdss/dp/slimport_custom_declare.h#L73

This address is 0x78 on my Nexus 5. Given [3] above it looks like we
need to support both addresses. What do you think about moving these
addresses into device tree?

Assuming that the device supports different addresses (I can't validate
that as I don't have access to the datasheet), and different addresses
need to be used on different systems, then the address to be used needs
to be provided by the firmware (DT in this case). Two options are
possible, either specifying the address explicitly in the device's DT
node, or specifying free addresses (in the form of a white list or black
list) and allocating an address from that pool. The latter has been
discussed in a BoF at the Linux Plumbers Conference last week,
https://linuxplumbersconf.org/event/4/contributions/542/.

quoted

The downstream and upstream kernel sources divide these addresses by two
to get the i2c address. Here's the code in upstream:

https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/bridge/analogix-anx78xx.c#L1353
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/bridge/analogix-anx78xx.c#L41

I'm not sure why the actual i2c address isn't used in this code.

The ANX7802/12/14/16 has a slave I2C bus that provides the interface to access
or control the chip from the AP. The I2C slave addresses used to control the
ANX7802/12/14/16 are 70h, 72h, 7Ah, 7Eh and 80h. Every address allows you to
access to different registers of the chip and AFAICS is not configurable.

I don't think these addresses should be configured via DT but for the driver itself.

My wild guess is that the ANX7808 has different addresses, but I don't have the
datasheet of this version.

I'm able to communicate with the 7808 on my Nexus 5 using the 0x78
address. Given that the addresses appear to be fixed per model, maybe it
makes sense to drop the address #defines and add the addresses to the
data pointer in the driver's of_match_table like so:

static const struct of_device_id anx78xx_match_table[] = {
        { .compatible = "analogix,anx7808", .data = PTR_TO_7808_ADDRS },
        { .compatible = "analogix,anx7812", .data = PTR_TO_781X_ADDRS },
        { .compatible = "analogix,anx7814", .data = PTR_TO_781X_ADDRS },
        { .compatible = "analogix,anx7818", .data = PTR_TO_781X_ADDRS },
        { /* sentinel */ },
};

Brian

I have spotted following comment on chromium's ML[1]:

The locations are hard coded in the register spec.  Furthermore, each
one can be changed independently--for example the Android driver puts
0x38 at 0x3c but leaves the rest alone.

It is not entirely clear, but IMO it suggests these addresses are
hardware configurable.


[1]:
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/44601/2/drivers/auxdisplay/slimport.c#331


Regards

Andrzej


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