Hi, On Wed, Dec 06, 2023 at 02:48:58PM +0200, Tomi Valkeinen wrote: > Hi mipi dsi maintainers (I'm not sure who that is =), > > On 21/09/2023 13:50, Tomi Valkeinen wrote: > > It's been reported that DSI host driver's detach can be called without > > the attach ever happening: > > > > https://lore.kernel.org/all/20230412073954.20601-1-tony@xxxxxxxxxxx/ > > > > After reading the code, I think this is what happens: > > > > We have a DSI host defined in the device tree and a DSI peripheral under > > that host (i.e. an i2c device using the DSI as data bus doesn't exhibit > > this behavior). > > > > The host driver calls mipi_dsi_host_register(), which causes (via a few > > functions) mipi_dsi_device_add() to be called for the DSI peripheral. So > > now we have a DSI device under the host, but attach hasn't been called. > > > > Normally the probing of the devices continues, and eventually the DSI > > peripheral's driver will call mipi_dsi_attach(), attaching the > > peripheral. > > > > However, if the host driver's probe encounters an error after calling > > mipi_dsi_host_register(), and before the peripheral has called > > mipi_dsi_attach(), the host driver will do cleanups and return an error > > from its probe function. The cleanups include calling > > mipi_dsi_host_unregister(). > > > > mipi_dsi_host_unregister() will call two functions for all its DSI > > peripheral devices: mipi_dsi_detach() and mipi_dsi_device_unregister(). > > The latter makes sense, as the device exists, but the former may be > > wrong as attach has not necessarily been done. > > > > To fix this, track the attached state of the peripheral, and only detach > > from mipi_dsi_host_unregister() if the peripheral was attached. > > > > Note that I have only tested this with a board with an i2c DSI > > peripheral, not with a "pure" DSI peripheral. > > > > However, slightly related, the unregister machinery still seems broken. > > E.g. if the DSI host driver is unbound, it'll detach and unregister the > > DSI peripherals. After that, when the DSI peripheral driver unbound > > it'll call detach either directly or using the devm variant, leading to > > a crash. And probably the driver will crash if it happens, for some > > reason, to try to send a message via the DSI bus. > > > > But that's another topic. > > > > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> > > --- > > Any comments? I can push this via drm-misc, but I'd like an ack. An ack is a requirement, it's not optional. Acked-by: Maxime Ripard <mripard@xxxxxxxxxx> Maxime
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