Why SCSI module needed for PCI-IDE ATA only disks ?

Why SCSI module needed for PCI-IDE ATA only disks ?

[Bernard Pidoux]

I am asking why need to compile the following modules while I do not
have any SCSI device ?

Modules Loaded

rose netrom mkiss ax25 crc16 mach64 drm nfsd exportfs lockd nfs_acl
sunrpc ipv6 snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq
ne2k_pci 8390 snd_pcm_oss snd_mixer_oss snd_ens1371 gameport snd_rawmidi
snd_seq_device snd_ac97_codec snd_ac97_bus af_packet snd_pcm snd_timer
snd_page_alloc snd soundcore floppy ide_cd binfmt_misc loop supermount

ahci ata_piix libata scsi_mod dm_mod

cpufreq_ondemand cpufreq_conservative cpufreq_powersave speedstep_lib
freq_table intel_agp agpgart uhci_hcd usbcore evdev tsdev ext3 jbd

Hardware is :

00:00.0 Host bridge: Intel Corporation 440BX/ZX/DX - 82443BX/ZX/DX Host
bridge (rev 03)
00:01.0 PCI bridge: Intel Corporation 440BX/ZX/DX - 82443BX/ZX/DX AGP
bridge (rev 03)
00:04.0 ISA bridge: Intel Corporation 82371AB/EB/MB PIIX4 ISA (rev 02)
00:04.1 IDE interface: Intel Corporation 82371AB/EB/MB PIIX4 IDE (rev 01)
00:04.2 USB Controller: Intel Corporation 82371AB/EB/MB PIIX4 USB (rev 01)
00:04.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 02)
00:0b.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8029(AS)
00:0c.0 Multimedia audio controller: Ensoniq ES1371 [AudioPCI-97] (rev 06)
00:0d.0 Mass storage controller: Promise Technology, Inc. PDC20262
(FastTrak66/Ultra66) (rev 01)
01:00.0 VGA compatible controller: ATI Technologies Inc 3D Rage Pro AGP
1X/2X (rev 5c)

ata_piix needs scsi_mod

When making menuconfig, the need to select SCSI submenu options seems
rather surprising to me for an IDE ATA disk only system.

Bernard Pidoux

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Phillip Susi]

Bernard Pidoux wrote:
> I am asking why need to compile the following modules while I do not
> have any SCSI device ?

Because your hardware is driven by a libata based driver.  This means it 
is a scsi bus driver and thus, requires mod_scsi and the scsi disk 
module to access disks on the bus.

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Jeff Garzik]

Bernard Pidoux wrote:
> I am asking why need to compile the following modules while I do not
> have any SCSI device ?

libata uses SCSI to provide a lot of infrastructure that it would 
otherwise have to recreate.  Also, using SCSI meant that it 
automatically worked in existing installers.

	Jeff

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Ed Sweetman]

Jeff Garzik wrote:
> Bernard Pidoux wrote:
>> I am asking why need to compile the following modules while I do not
>> have any SCSI device ?
>
> libata uses SCSI to provide a lot of infrastructure that it would 
> otherwise have to recreate.  Also, using SCSI meant that it 
> automatically worked in existing installers.
>
>     Jeff
>
This confusion could easily be remedied by explaining the requirement in 
the Help output for libata drivers/section.  Also, making a dependency 
in the menu (since there is one) or automatically selecting the required 
scsi items when you select a libata driver would seem logical. As it is, 
nothing is said of scsi requirements in menuconfig. Trying to boot a 
machine without compiling the scsi drivers (something you're allowed to 
do) results in a system that boots and initializes the ata busses but 
can't communicate to any of the drives on them, (useless).


Then maybe later down the road, moving those scsi drivers shared by scsi 
and libata to the generic block layer would seem logical. That is, when 
ide is gone from the kernel and all the kernel speaks is scsi, there 
would be no need to differentiate scsi from the generic block layer 
devices, and no need to compile "scsi" drivers to have libata driver 
support, eliminating any possible further confusion.

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Robert Hancock]

Ed Sweetman wrote:
> Jeff Garzik wrote:
>> Bernard Pidoux wrote:
>>> I am asking why need to compile the following modules while I do not
>>> have any SCSI device ?
>>
>> libata uses SCSI to provide a lot of infrastructure that it would 
>> otherwise have to recreate.  Also, using SCSI meant that it 
>> automatically worked in existing installers.
>>
>>     Jeff
>>
> This confusion could easily be remedied by explaining the requirement in 
> the Help output for libata drivers/section.  Also, making a dependency 
> in the menu (since there is one) or automatically selecting the required 
> scsi items when you select a libata driver would seem logical. As it is, 
> nothing is said of scsi requirements in menuconfig. Trying to boot a 
> machine without compiling the scsi drivers (something you're allowed to 
> do) results in a system that boots and initializes the ata busses but 
> can't communicate to any of the drives on them, (useless).

You can't select libata drivers without the SCSI core. However, you can 
select libata drivers without the SCSI disk (sd) or the SCSI CD (sr) 
drivers. However, that's a legitimate configuration as you may have only 
hard disks, only CD drives, etc. and there would be no need to build the 
other module. This isn't a major problem for most standard 
configurations as those drivers are needed to handle things like USB and 
FireWire flash drives, external HDs/optical drives, etc. anyway.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Ed Sweetman]

Robert Hancock wrote:
> Ed Sweetman wrote:
>> Jeff Garzik wrote:
>>> Bernard Pidoux wrote:
>>>> I am asking why need to compile the following modules while I do not
>>>> have any SCSI device ?
>>>
>>> libata uses SCSI to provide a lot of infrastructure that it would 
>>> otherwise have to recreate.  Also, using SCSI meant that it 
>>> automatically worked in existing installers.
>>>
>>>     Jeff
>>>
>> This confusion could easily be remedied by explaining the requirement 
>> in the Help output for libata drivers/section.  Also, making a 
>> dependency in the menu (since there is one) or automatically 
>> selecting the required scsi items when you select a libata driver 
>> would seem logical. As it is, nothing is said of scsi requirements in 
>> menuconfig. Trying to boot a machine without compiling the scsi 
>> drivers (something you're allowed to do) results in a system that 
>> boots and initializes the ata busses but can't communicate to any of 
>> the drives on them, (useless).
>
> You can't select libata drivers without the SCSI core. However, you 
> can select libata drivers without the SCSI disk (sd) or the SCSI CD 
> (sr) drivers. However, that's a legitimate configuration as you may 
> have only hard disks, only CD drives, etc. and there would be no need 
> to build the other module. This isn't a major problem for most 
> standard configurations as those drivers are needed to handle things 
> like USB and FireWire flash drives, external HDs/optical drives, etc. 
> anyway.
>
What's not a legitimate configuration is libata drivers, no low level 
scsi drivers, no ide drivers and no sd,sr,sg drivers.  Yet, that is the 
configuration the kernel currently gives you. How is that more correct 
than any of the 3 solutions I have suggested?

The point is there is nothing in the help section in libata to tell you 
that these "scsi" drivers are needed for disk / cdrom / generic device 
access in libata.  Indeed, there is no obvious connection to the two. 

Either configuration options need to be put in the libata directory that 
would just select the drivers (libata disk, cdrom, generic configuration 
options which would just enable the appropriate config variable, in 
other words in the menu config have two config directives which would 
enable the same drivers but be under different submenus to avoid 
confusion), or a short description in the help dialog to tell users that 
they have to enable those scsi drivers under the scsi section to use 
their drivers under the libata section.  

It's not safe to assume people will have those drivers compiled because 
of usb or firewire or flash drives.  Assuming that situation is 10 times 
more problematic than any possible argument against just selecting those 
scsi drivers automatically and letting the user  deselect them as needed 
when they select a libata driver.


Personaly, I prefer a help dialog blurb explaining that the user has to 
enable certain scsi drivers to actually use their libata driven 
devices.    That, at the very least, I believe is necessary and not 
asking much.  

I've made patches before that impliment these trivial features in 
menuconfig. In the grand scheme of things this isn't that important to 
kernel development, but it's going to get more and more feedback as more 
people move to libata and eventually it will be fixed in some manner 
similar to those i've mentioned, I think it would just be better to do 
it now than wait until the mailing list is filled with end users asking 
why they need scsi when they obviously only have sata/ide and want to 
use libata.

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Robert Hancock]

Ed Sweetman wrote:
> What's not a legitimate configuration is libata drivers, no low level 
> scsi drivers, no ide drivers and no sd,sr,sg drivers.  Yet, that is the 
> configuration the kernel currently gives you. How is that more correct 
> than any of the 3 solutions I have suggested?

You can't build libata without low-level SCSI drivers. CONFIG_ATA 
automatically selects CONFIG_SCSI.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

Re: Why SCSI module needed for PCI-IDE ATA only disks ?

[Ed Sweetman]

Robert Hancock wrote:
> Ed Sweetman wrote:
>> What's not a legitimate configuration is libata drivers, no low level 
>> scsi drivers, no ide drivers and no sd,sr,sg drivers.  Yet, that is 
>> the configuration the kernel currently gives you. How is that more 
>> correct than any of the 3 solutions I have suggested?
>
> You can't build libata without low-level SCSI drivers. CONFIG_ATA 
> automatically selects CONFIG_SCSI.
>
config scsi isn't low level.  There are no scsi controllers selected by 
selecting config_ata. Mening, that the user hasn't bothered going into 
the SCSI section.  In effect you have a system that detects the ata 
controllers but nothing that can use the drives on them. How is that a 
valid system, a system where no drives are usable, but having some 
mention of the configuration in the Help of libata or automatically 
selecting those scsi_sd, sr, and sg drivers and letting the user 
deselect them as needed instead of the other way around Not a valid are 
more correct system?  

No matter what when you select a scsi controller or libata controller 
you are going to need to select one or more of those scsi device drivers 
(sr,sg,sd) the issue is that when you are only using libata, you have no 
reason to bother with the scsi section so it's not readily apparent that 
you would need those block device drivers.   I'm not saying we should 
auto select them, but I am saying that auto selecting is way better than 
keeping the kernel configuration the way it is and selecting none.



In the end the problem is in the layout of the config.  SCSI is _THE_ 
device interface protocol but most people dont have scsi physical 
interfaces. The kernel differentiates between the two inside the SCSI 
section.  This made sense before ide was marked for eventual replacement 
by libata. Now everything uses that scsi top level for block device 
access.  That effectively makes those scsi block devices generic block 
devices.  SCSI and LIBATA sections should have configuration options 
that are relevant to those physical devices and interfaces and not 
require options from eachother's sections to get drivers in their own 
sections to work.   Massively shared config options shouldn't be stuck 
in some sub menu below where all the things that use it are located.
But that's for some much later version of the kernel to deal with (when 
ide is removed and such).