[RFC] drm/bridge: adv7533: remove dynamic lane switching from adv7533 bridge
Dmitry Baryshkov
dmitry.baryshkov at linaro.org
Fri Aug 26 10:17:43 UTC 2022
On 22/08/2022 19:31, Dmitry Baryshkov wrote:
> On 09/08/2022 22:40, Laurent Pinchart wrote:
>> Hi Abhinav,
>>
>> Thank you for the patch.
>>
>> On Mon, Aug 08, 2022 at 05:35:30PM -0700, Abhinav Kumar wrote:
>>> adv7533 bridge tries to dynamically switch lanes based on the
>>> mode by detaching and attaching the mipi dsi device.
>>>
>>> This approach is incorrect because as per the DSI spec the
>>> number of lanes is fixed at the time of system design or initial
>>> configuration and may not change dynamically.
>>
>> Is that really so ? The number of lanes connected on the board is
>> certainlyset at design time, but a lower number of lanes can be used at
>> runtime. It shouldn't change dynamically while the display is on, but it
>> could change at mode set time.
>
> I'm not sure if I interpreted the standard correctly, but I tended to
> have the same interpretation as Abhinav did.
>
> Anyway, even if we allow the drivers to switch the amount of lanes, this
> should not happen in the form of detach()/attach() cycle. The drivers
> use mipi_dsi_attach() as way to signal the DSI hosts that the sink
> device is ready. Some of DSI hosts (including MSM one) would bind
> components from the attach callback.
>
> If we were to support dynamically changing the amount of lanes, I would
> ask for additional mipi_dsi API call telling the host to switch the
> amount of lanes. And note that this can open the can of worms. Different
> hosts might have different requirements here. For example for the MSM
> platform the amount of lanes is programmed during bridge_pre_enable
> chain call, so it is possible to just set the amount of lanes following
> the msm_dsi_device::lanes. Other hosts might have other requirements.
>
> Thus said I'd suggest accepting this patch and maybe working on the
> API/support for the lane switching as a followup.
Laurent, gracious ping for your response.
>
>
>>
>>> In addition this method of dynamic switch of detaching and
>>> attaching the mipi dsi device also results in removing
>>> and adding the component which is not necessary.
>>
>> Yes, that doesn't look good, and the .mode_valid() operation is
>> definitely not the right point where to set the number of lanes.
>
> .mode_set()?
>
>>
>>> This approach is also prone to deadlocks. So for example, on the
>>> db410c whenever this path is executed with lockdep enabled,
>>> this results in a deadlock due to below ordering of locks.
>
> Even without the deadlock, we are pulling the whole DRM device from
> beneath the DSI panel by unbinding all the components. This is not going
> to work correctly.
>
>>>
>>> -> #1 (crtc_ww_class_acquire){+.+.}-{0:0}:
>>> lock_acquire+0x6c/0x90
>>> drm_modeset_acquire_init+0xf4/0x150
>>> drmm_mode_config_init+0x220/0x770
>>> msm_drm_bind+0x13c/0x654
>>> try_to_bring_up_aggregate_device+0x164/0x1d0
>>> __component_add+0xa8/0x174
>>> component_add+0x18/0x2c
>>> dsi_dev_attach+0x24/0x30
>>> dsi_host_attach+0x98/0x14c
>>> devm_mipi_dsi_attach+0x38/0xb0
>>> adv7533_attach_dsi+0x8c/0x110
>>> adv7511_probe+0x5a0/0x930
>>> i2c_device_probe+0x30c/0x350
>>> really_probe.part.0+0x9c/0x2b0
>>> __driver_probe_device+0x98/0x144
>>> driver_probe_device+0xac/0x14c
>>> __device_attach_driver+0xbc/0x124
>>> bus_for_each_drv+0x78/0xd0
>>> __device_attach+0xa8/0x1c0
>>> device_initial_probe+0x18/0x24
>>> bus_probe_device+0xa0/0xac
>>> deferred_probe_work_func+0x90/0xd0
>>> process_one_work+0x28c/0x6b0
>>> worker_thread+0x240/0x444
>>> kthread+0x110/0x114
>>> ret_from_fork+0x10/0x20
>>>
>>> -> #0 (component_mutex){+.+.}-{3:3}:
>>> __lock_acquire+0x1280/0x20ac
>>> lock_acquire.part.0+0xe0/0x230
>>> lock_acquire+0x6c/0x90
>>> __mutex_lock+0x84/0x400
>>> mutex_lock_nested+0x3c/0x70
>>> component_del+0x34/0x170
>
>>> dsi_dev_detach+0x24/0x30
>>> dsi_host_detach+0x20/0x64
>>> mipi_dsi_detach+0x2c/0x40
>>> adv7533_mode_set+0x64/0x90
>>> adv7511_bridge_mode_set+0x210/0x214
>>> drm_bridge_chain_mode_set+0x5c/0x84
>>> crtc_set_mode+0x18c/0x1dc
>>> drm_atomic_helper_commit_modeset_disables+0x40/0x50
>>> msm_atomic_commit_tail+0x1d0/0x6e0
>>> commit_tail+0xa4/0x180
>>> drm_atomic_helper_commit+0x178/0x3b0
>>> drm_atomic_commit+0xa4/0xe0
>>> drm_client_modeset_commit_atomic+0x228/0x284
>>> drm_client_modeset_commit_locked+0x64/0x1d0
>>> drm_client_modeset_commit+0x34/0x60
>>> drm_fb_helper_lastclose+0x74/0xcc
>>> drm_lastclose+0x3c/0x80
>>> drm_release+0xfc/0x114
>>> __fput+0x70/0x224
>>> ____fput+0x14/0x20
>>> task_work_run+0x88/0x1a0
>>> do_exit+0x350/0xa50
>>> do_group_exit+0x38/0xa4
>>> __wake_up_parent+0x0/0x34
>>> invoke_syscall+0x48/0x114
>>> el0_svc_common.constprop.0+0x60/0x11c
>>> do_el0_svc+0x30/0xc0
>>> el0_svc+0x58/0x100
>>> el0t_64_sync_handler+0x1b0/0x1bc
>>> el0t_64_sync+0x18c/0x190
>>>
>>> Due to above reasons, remove the dynamic lane switching
>>> code from adv7533 bridge chip and filter out the modes
>>> which would need different number of lanes as compared
>>> to the initialization time using the mode_valid callback.
>>>
>>> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
>>> ---
>>> drivers/gpu/drm/bridge/adv7511/adv7511.h | 3 ++-
>>> drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 18 ++++++++++++++----
>>> drivers/gpu/drm/bridge/adv7511/adv7533.c | 25
>>> +++++++++++++------------
>>> 3 files changed, 29 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511.h
>>> b/drivers/gpu/drm/bridge/adv7511/adv7511.h
>>> index 9e3bb8a8ee40..0a7cec80b75d 100644
>>> --- a/drivers/gpu/drm/bridge/adv7511/adv7511.h
>>> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511.h
>>> @@ -417,7 +417,8 @@ static inline int adv7511_cec_init(struct device
>>> *dev, struct adv7511 *adv7511)
>>> void adv7533_dsi_power_on(struct adv7511 *adv);
>>> void adv7533_dsi_power_off(struct adv7511 *adv);
>>> -void adv7533_mode_set(struct adv7511 *adv, const struct
>>> drm_display_mode *mode);
>>> +enum drm_mode_status adv7533_mode_valid(struct adv7511 *adv,
>>> + const struct drm_display_mode *mode);
>>> int adv7533_patch_registers(struct adv7511 *adv);
>>> int adv7533_patch_cec_registers(struct adv7511 *adv);
>>> int adv7533_attach_dsi(struct adv7511 *adv);
>>> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>> b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>> index 5bb9300040dd..1115ef9be83c 100644
>>> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
>>> @@ -697,7 +697,7 @@ adv7511_detect(struct adv7511 *adv7511, struct
>>> drm_connector *connector)
>>> }
>>> static enum drm_mode_status adv7511_mode_valid(struct adv7511
>>> *adv7511,
>>> - struct drm_display_mode *mode)
>>> + const struct drm_display_mode *mode)
>>> {
>>> if (mode->clock > 165000)
>>> return MODE_CLOCK_HIGH;
>>> @@ -791,9 +791,6 @@ static void adv7511_mode_set(struct adv7511
>>> *adv7511,
>>> regmap_update_bits(adv7511->regmap, 0x17,
>>> 0x60, (vsync_polarity << 6) | (hsync_polarity << 5));
>>> - if (adv7511->type == ADV7533 || adv7511->type == ADV7535)
>>> - adv7533_mode_set(adv7511, adj_mode);
>>> -
>>> drm_mode_copy(&adv7511->curr_mode, adj_mode);
>>> /*
>>> @@ -913,6 +910,18 @@ static void adv7511_bridge_mode_set(struct
>>> drm_bridge *bridge,
>>> adv7511_mode_set(adv, mode, adj_mode);
>>> }
>>> +static enum drm_mode_status adv7511_bridge_mode_valid(struct
>>> drm_bridge *bridge,
>>> + const struct drm_display_info *info,
>>> + const struct drm_display_mode *mode)
>>> +{
>>> + struct adv7511 *adv = bridge_to_adv7511(bridge);
>>> +
>>> + if (adv->type == ADV7533 || adv->type == ADV7535)
>>> + return adv7533_mode_valid(adv, mode);
>>> + else
>>> + return adv7511_mode_valid(adv, mode);
>>> +}
>>> +
>>> static int adv7511_bridge_attach(struct drm_bridge *bridge,
>>> enum drm_bridge_attach_flags flags)
>>> {
>>> @@ -960,6 +969,7 @@ static const struct drm_bridge_funcs
>>> adv7511_bridge_funcs = {
>>> .enable = adv7511_bridge_enable,
>>> .disable = adv7511_bridge_disable,
>>> .mode_set = adv7511_bridge_mode_set,
>>> + .mode_valid = adv7511_bridge_mode_valid,
>>> .attach = adv7511_bridge_attach,
>>> .detect = adv7511_bridge_detect,
>>> .get_edid = adv7511_bridge_get_edid,
>>> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7533.c
>>> b/drivers/gpu/drm/bridge/adv7511/adv7533.c
>>> index ef6270806d1d..4a6d45edf431 100644
>>> --- a/drivers/gpu/drm/bridge/adv7511/adv7533.c
>>> +++ b/drivers/gpu/drm/bridge/adv7511/adv7533.c
>>> @@ -100,26 +100,27 @@ void adv7533_dsi_power_off(struct adv7511 *adv)
>>> regmap_write(adv->regmap_cec, 0x27, 0x0b);
>>> }
>>> -void adv7533_mode_set(struct adv7511 *adv, const struct
>>> drm_display_mode *mode)
>>> +enum drm_mode_status adv7533_mode_valid(struct adv7511 *adv,
>>> + const struct drm_display_mode *mode)
>>> {
>>> + int lanes;
>>> struct mipi_dsi_device *dsi = adv->dsi;
>>> - int lanes, ret;
>>> -
>>> - if (adv->num_dsi_lanes != 4)
>>> - return;
>>> if (mode->clock > 80000)
>>> lanes = 4;
>>> else
>>> lanes = 3;
>>> - if (lanes != dsi->lanes) {
>>> - mipi_dsi_detach(dsi);
>>> - dsi->lanes = lanes;
>>> - ret = mipi_dsi_attach(dsi);
>>> - if (ret)
>>> - dev_err(&dsi->dev, "failed to change host lanes\n");
>>> - }
>>> + /*
>>> + * number of lanes cannot be changed after initialization
>>> + * as per section 6.1 of the DSI specification. Hence filter
>>> + * out the modes which shall need different number of lanes
>>> + * than what was configured in the device tree.
>>> + */
>>> + if (lanes != dsi->lanes)
>>> + return MODE_BAD;
>>> +
>>> + return MODE_OK;
>>> }
>>> int adv7533_patch_registers(struct adv7511 *adv)
>>
>
--
With best wishes
Dmitry
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