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Message-ID: <63bae3ec-2bbf-f4f7-b54a-73a921f8f438@quicinc.com>
Date: Thu, 6 Jan 2022 09:13:45 -0800
From: Kuogee Hsieh <quic_khsieh@...cinc.com>
To: Stephen Boyd <swboyd@...omium.org>, <agross@...nel.org>,
<airlied@...ux.ie>, <bjorn.andersson@...aro.org>,
<daniel@...ll.ch>, <dmitry.baryshkov@...aro.org>,
<robdclark@...il.com>, <sean@...rly.run>, <vkoul@...nel.org>
CC: <quic_abhinavk@...cinc.com>, <aravindh@...eaurora.org>,
<quic_sbillaka@...cinc.com>, <freedreno@...ts.freedesktop.org>,
<dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/msm/dp: populate connector of struct dp_panel
On 1/5/2022 1:34 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2021-12-29 11:17:02)
>> There is kernel crashed due to unable to handle kernel NULL
>> pointer dereference of dp_panel->connector while running DP link
>> layer compliance test case 4.2.2.6 (EDID Corruption Detection).
> Can you explain how we get into that situation? Like
>
> "We never assign struct dp_panel::connector, instead the connector is
> stored in struct msm_dp::connector. When we run compliance testing test
> case 4.2.2.6 dp_panel_handle_sink_request() won't have a valid edid set
> in struct dp_panel::edid so we'll try to use the connectors
> real_edid_checksum and hit a NULL pointer deref error because the
> connector pointer is never assigned."
>
>> This patch fixes this problem by populating connector of dp_panel.
>>
>> [drm:dp_panel_read_sink_caps] *ERROR* panel edid read failed
>> Unable to handle kernel NULL pointer dereference at virtual address 00000000000006e1
>> Mem abort info:
>> ESR = 0x96000006
>> EC = 0x25: DABT (current EL), IL = 32 bits
>> SET = 0, FnV = 0
>> EA = 0, S1PTW = 0
>> Data abort info:
>> ISV = 0, ISS = 0x00000006
>> CM = 0, WnR = 0
>> user pgtable: 4k pages, 39-bit VAs, pgdp=0000000115f25000
>> [00000000000006e1] pgd=00000001174fe003, p4d=00000001174fe003, pud=00000001174fe003, pmd=0000000000000000
>> Internal error: Oops: 96000006 [#1] PREEMPT SMP
> This sort of stuff isn't really useful because it takes quite a few
> lines to say "We hit a NULL pointer deref" which was already stated. I'd
> rather have a clear description of what goes wrong and how setting the
> pointer in msm_dp_modeset_init() fixes it.
>
>> {...]
>>
>> Changes in V2:
>> -- populate panel connector at msm_dp_modeset_init() instead of at dp_panel_read_sink_caps()
>>
>> Fixes: 7948fe12d47 ("drm/msm/dp: return correct edid checksum after corrupted edid checksum read")
>> Signee-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>> ---
>> drivers/gpu/drm/msm/dp/dp_display.c | 25 +++++++++++++++----------
>> 1 file changed, 15 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
>> index 3449d3f..c282bbf 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>> @@ -1495,36 +1495,41 @@ void msm_dp_debugfs_init(struct msm_dp *dp_display, struct drm_minor *minor)
>> }
>> }
>>
>> -int msm_dp_modeset_init(struct msm_dp *dp_display, struct drm_device *dev,
>> +int msm_dp_modeset_init(struct msm_dp *dp, struct drm_device *dev,
>> struct drm_encoder *encoder)
>> {
>> struct msm_drm_private *priv;
>> + struct dp_display_private *dp_display;
>> int ret;
>>
>> - if (WARN_ON(!encoder) || WARN_ON(!dp_display) || WARN_ON(!dev))
>> + if (WARN_ON(!encoder) || WARN_ON(!dp) || WARN_ON(!dev))
>> return -EINVAL;
>>
>> priv = dev->dev_private;
>> - dp_display->drm_dev = dev;
>> + dp->drm_dev = dev;
>> +
>> + dp_display = container_of(dp, struct dp_display_private, dp_display);
>>
>> - ret = dp_display_request_irq(dp_display);
>> + ret = dp_display_request_irq(dp);
>> if (ret) {
>> DRM_ERROR("request_irq failed, ret=%d\n", ret);
>> return ret;
>> }
>>
>> - dp_display->encoder = encoder;
>> + dp->encoder = encoder;
>>
>> - dp_display->connector = dp_drm_connector_init(dp_display);
>> - if (IS_ERR(dp_display->connector)) {
>> - ret = PTR_ERR(dp_display->connector);
>> + dp->connector = dp_drm_connector_init(dp);
>> + if (IS_ERR(dp->connector)) {
>> + ret = PTR_ERR(dp->connector);
>> DRM_DEV_ERROR(dev->dev,
>> "failed to create dp connector: %d\n", ret);
>> - dp_display->connector = NULL;
>> + dp->connector = NULL;
>> return ret;
>> }
>>
>> - priv->connectors[priv->num_connectors++] = dp_display->connector;
>> + dp_display->panel->connector = dp->connector;
> This is the one line that matters I think? Can we reach the connector
> for the dp device without going through the panel in
> dp_panel_handle_sink_request()? That would reduce the number of struct
> elements if possible.
I tried, but very difficulty. It will take more text section space.
>
>> +
>> + priv->connectors[priv->num_connectors++] = dp->connector;
> Can we not rename all the local variables in this patch and do it later
> or never? Reading this patch takes a long time because we have to make
> sure nothing has actually changed with the rename of 'dp_display' to
> 'dp'.
>
>> return 0;
>> }
>>
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> a Linux Foundation Collaborative Project
>>
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