[PATCH 4/5] gpu: host1x: Provide a proper struct bus_type

[Mark Zhang]

Thanks for the explanation.

Reviewed-by: Mark Zhang <markz at nvidia.com>

Mark
On 01/05/2015 10:49 PM, Thierry Reding wrote:
> * PGP Signed by an unknown key
> 
> On Tue, Dec 23, 2014 at 03:30:20PM +0800, Mark Zhang wrote:
>> On 12/19/2014 11:24 PM, Thierry Reding wrote:
>>> From: Thierry Reding <treding at nvidia.com>
>>>
>>> Previously the struct bus_type exported by the host1x infrastructure was
>>> only a very basic skeleton. Turn that implementation into a more full-
>>> fledged bus to support proper probe ordering and power management.
>>>
>>> Note that the bus infrastructure needs to be available before any of the
>>> drivers can be registered, so the bus needs to be registered before the
>>> host1x module. Otherwise drivers could be registered before the module
>>> is loaded and trigger a BUG_ON() in driver_register(). To ensure the bus
>>> infrastructure is always there, always build the code into the kernel
>>> when enabled and register it with a postcore initcall.
>>>
>>
>> So this means there is no chance that host1x can be built as a kernel
>> module, right? I'm fine with that, just asking.
> 
> No, it means that not all of host1x can be built as a module. The host1x
> bus infrastructure will always be built-in when TEGRA_HOST1X is enabled.
> 
>>> Signed-off-by: Thierry Reding <treding at nvidia.com>
>>> ---
>> [...]
>>> diff --git a/drivers/gpu/host1x/Makefile b/drivers/gpu/host1x/Makefile
>>> index c1189f004441..a3e667a1b6f5 100644
>>> --- a/drivers/gpu/host1x/Makefile
>>> +++ b/drivers/gpu/host1x/Makefile
>>> @@ -1,5 +1,4 @@
>>>  host1x-y = \
>>> -	bus.o \
>>>  	syncpt.o \
>>>  	dev.o \
>>>  	intr.o \
>>> @@ -13,3 +12,5 @@ host1x-y = \
>>>  	hw/host1x04.o
>>>  
>>>  obj-$(CONFIG_TEGRA_HOST1X) += host1x.o
>>> +
>>> +obj-y += bus.o
>>
>> I didn't get it, why we need to do this?
> 
> If CONFIG_TEGRA_HOST1X=m, then obj-$(CONFIG_TEGRA_HOST1X) builds the
> bus.o into a module. But we want it to always be built-in. The build
> system will descend into the drivers/gpu/host1x directory only if the
> TEGRA_HOST1X symbol is selected (either =y or =m), therefore obj-y here
> will result in bus.o being built-in whether the rest of host1x is built
> as a module or built-in.
> 
>>> diff --git a/drivers/gpu/host1x/bus.c b/drivers/gpu/host1x/bus.c
>>> index 0b52f0ea8871..28630a5e9397 100644
>>> --- a/drivers/gpu/host1x/bus.c
>>> +++ b/drivers/gpu/host1x/bus.c
>>> @@ -72,13 +72,14 @@ static void host1x_subdev_del(struct host1x_subdev *subdev)
>> [...]
>>>  
>>>  static inline struct host1x_device *to_host1x_device(struct device *dev)
>>>
>>
>> The change looks good to me. Just one thing I feel not comfortable:
>> "struct host1x_device" is not a real device, it represents the drm
>> device actually. The real tegra host1x device is represented by "struct
>> host1x". But the name "host1x_device" makes people confusing, I mean, it
>> will make people thinking it's the real "tegra host1x" device then bring
>> the reading difficulty.
> 
> The reason behind that name is that host1x provides a bus (real to some
> degree, but also virtual). host1x is the device that provides the bus
> whereas a host1x_device is a "device" on the "host1x" bus. That's just
> like an i2c_client is a "client" on the "I2C" bus. Or an spi_device is a
> "device" on the "SPI" bus.
> 
>> Why don't we change this to something like "drm_device" or
>> "tegra_drm_device"?
> 
> Other devices can be host1x devices. Some time ago work was being done
> on a driver for the CSI/VI hardware (for camera or video input). The
> idea was that it would also be instantiated as a host1x_device in some
> other subsystem (V4L2 at the time).
> 
> The functionality here is generic and in no way DRM specific.
> 
> Thierry
> 
> * Unknown Key
> * 0x7F3EB3A1
>