On Tue, 06 May 2008 16:34:27 +0200
Stefan Richter <stefanr@s5r6.in-berlin.de> wrote:
True, unfortunately.
This is easy to maintain, if you have just a few selects, but this is not the
case of V4L drivers. Look some examples:
IVTV driver:
config VIDEO_IVTV
tristate "Conexant cx23416/cx23415 MPEG encoder/decoder support"
depends on VIDEO_V4L1 && VIDEO_V4L2 && PCI && I2C && EXPERIMENTAL
select I2C_ALGOBIT
select FW_LOADER
select VIDEO_IR
select MEDIA_TUNER
select VIDEO_TVEEPROM
select VIDEO_CX2341X
select VIDEO_CX25840
select VIDEO_MSP3400
select VIDEO_SAA711X
select VIDEO_SAA717X
select VIDEO_SAA7127
select VIDEO_TVAUDIO
select VIDEO_CS53L32A
select VIDEO_M52790
select VIDEO_WM8775
select VIDEO_WM8739
select VIDEO_VP27SMPX
select VIDEO_UPD64031A
select VIDEO_UPD64083
config VIDEO_FB_IVTV
tristate "Conexant cx23415 framebuffer support"
depends on VIDEO_IVTV && FB && EXPERIMENTAL
select FB_CFB_FILLRECT
select FB_CFB_COPYAREA
select FB_CFB_IMAGEBLIT
(btw, on above, IVTV is missing INPUT)
This is Cx88 driver:
config VIDEO_CX88
tristate "Conexant 2388x (bt878 successor) support"
depends on VIDEO_DEV && PCI && I2C && INPUT
select I2C_ALGOBIT
select FW_LOADER
select VIDEO_BTCX
select VIDEOBUF_DMA_SG
select MEDIA_TUNER
select VIDEO_TVEEPROM
select VIDEO_IR
select VIDEO_WM8775 if VIDEO_HELPER_CHIPS_AUTO
config VIDEO_CX88_ALSA
tristate "Conexant 2388x DMA audio support"
depends on VIDEO_CX88 && SND && EXPERIMENTAL
select SND_PCM
config VIDEO_CX88_BLACKBIRD
tristate "Blackbird MPEG encoder support (cx2388x + cx23416)"
depends on VIDEO_CX88
select VIDEO_CX2341X
config VIDEO_CX88_DVB
tristate "DVB/ATSC Support for cx2388x based TV cards"
depends on VIDEO_CX88 && DVB_CORE
select VIDEOBUF_DVB
select DVB_PLL if !DVB_FE_CUSTOMISE
select DVB_MT352 if !DVB_FE_CUSTOMISE
select DVB_ZL10353 if !DVB_FE_CUSTOMISE
select DVB_OR51132 if !DVB_FE_CUSTOMISE
select DVB_CX22702 if !DVB_FE_CUSTOMISE
select DVB_LGDT330X if !DVB_FE_CUSTOMISE
select DVB_NXT200X if !DVB_FE_CUSTOMISE
select DVB_CX24123 if !DVB_FE_CUSTOMISE
select DVB_ISL6421 if !DVB_FE_CUSTOMISE
select MEDIA_TUNER_SIMPLE if !DVB_FE_CUSTOMISE
select DVB_S5H1411 if !DVB_FE_CUSTOMISE
(here, FW_LOADER is at the wrong sub-driver - it should be at CX88_DVB - and
HOTPLUG dependency is missing)
Ok, most of those select's have the same set of dependencies. Yet, it is really
hard to maintain. The result is that almost every new driver has some missing
dependencies.
Those two drivers are just two examples where I found some bugs today. Most of
the drivers have dozens of select.
You may argue to not use select, but it is really hard to avoid, since each of
those main drivers (cx88, ivtv, bttv, etc) supports a large number of different
devices, that needs different chips. Most V4L/DVB devices has an internal I2C
bus that gives the flexibility for the board manufacturers to add/replace the
internal components at the i2c bus. So, the Kernel uses abstraction layers that
allows that the same driver to use different internal components.
What the Kbuild system does is to autoselect, by default, all drivers that
might be needed, in order to support all variants. At runtime (if module), only
the drivers effectively needed will be loaded. Advanced users have the option
of manually select the needed drivers, if they are 100% sure of what their
device needs (generally, this is valuable only for embedded systems).
Cheers,
Mauro
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