Messages in this thread | | | Subject | Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Sun, 23 Feb 2020 20:45:23 -0800 |
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On 2/20/20 11:11 AM, Sowjanya Komatineni wrote: > > On 2/20/20 5:33 AM, Hans Verkuil wrote: >> External email: Use caution opening links or attachments >> >> >> (Replying to myself so I can explain this a bit more) >> >> On 2/20/20 1:44 PM, Hans Verkuil wrote: >>>> + >>>> +static int tegra_csi_tpg_channels_alloc(struct tegra_csi *csi) >>>> +{ >>>> + struct device_node *node = csi->dev->of_node; >>>> + unsigned int port_num; >>>> + int ret; >>>> + struct tegra_csi_channel *item; >>>> + unsigned int tpg_channels = csi->soc->csi_max_channels; >>>> + >>>> + /* allocate CSI channel for each CSI x2 ports */ >>>> + for (port_num = 0; port_num < tpg_channels; port_num++) { >>>> + item = devm_kzalloc(csi->dev, sizeof(*item), GFP_KERNEL); >>> Using devm_*alloc can be dangerous. If someone unbinds the driver, then >>> all memory allocated with devm_ is immediately freed. But if an >>> application >>> still has a filehandle open, then when it closes it it might still >>> reference >>> this already-freed memory. >>> >>> I recommend that you avoid using devm_*alloc for media drivers. >> A good test is to unbind & bind the driver: >> >> cd /sys/devices/platform/50000000.host1x/54080000.vi/driver >> echo -n 54080000.vi >unbind >> echo -n 54080000.vi >bind >> >> First just do this without the driver being used. That already >> gives me 'list_del corruption' kernel messages (list debugging >> is turned on in my kernel).
Will fix in v4 to use kzalloc and also proper release v4l2 to make sure unbind/bind works properly.
BTW, tegra vi and csi are registered as clients to host1x video driver.
So, unbind and bind should be done with host1x video driver "tegra-video"
cd /sys/devices/platform/50000000.host1x/tegra-video/driver echo -n tegra-video > unbind echo -n tegra-video > bind
>> >> Note that this first test is basically identical to a rmmod/modprobe >> of the driver. But when I compiled the driver as a module it didn't >> create any video device nodes! Nor did I see any errors in the kernel >> log. I didn't pursue this, and perhaps I did something wrong, but it's >> worth taking a look at. >> >> The next step would be to have a video node open with: >> >> v4l2-ctl --sleep 10 >> >> then while it is sleeping unbind the driver and see what happens >> when v4l2-ctl exits. >> >> Worst case is when you are streaming: >> >> v4l2-ctl --stream-mmap >> >> and then unbind. >> >> In general, the best way to get this to work correctly is: >> >> 1) don't use devm_*alloc >> 2) set the release callback of struct v4l2_device and do all freeing >> there. >> 3) in the platform remove() callback you call media_device_unregister() >> and video_unregister_device(). > Reg 3, in current patch, media_device_unregister is called in > host1x_video_remove > video_unregister_device happens during host1x_video_remove -> > host1x_device_exit -> tegra_vi_exit -> tegra_vi_channels_cleanup > >> It's worth getting this right in this early stage, rather than fixing it >> in the future. >> >> Regards, >> >> Hans
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