Re: [PATCH] arm: omap: reduce zImage size on omap2plus_defconfig

[Igor Grinberg <grinberg@compulab.co.il>]

Hi Tony,

On 12/24/14 21:04, Tony Lindgren wrote:
> * Felipe Balbi <balbi@ti.com> [141224 07:52]:
>> Hi,
>>
>> On Wed, Dec 24, 2014 at 01:53:46PM +0200, Igor Grinberg wrote:
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> On 12/23/14 18:19, Felipe Balbi wrote:
>>>> On Tue, Dec 23, 2014 at 09:30:45AM +0200, Igor Grinberg wrote:
>>>>> Hi Felipe,
>>>>>
>>>>> On 12/22/14 20:05, Felipe Balbi wrote:
>>>>>
>>>>> [...]
>>>>>
>>>>>>  CONFIG_SCSI_SCAN_ASYNC=y
>>>>>> -CONFIG_ATA=y
>>>>>> -CONFIG_SATA_AHCI_PLATFORM=y
>>>>>> -CONFIG_MD=y
>>>>>> +CONFIG_ATA=m
>>>>>> +CONFIG_SATA_AHCI_PLATFORM=m
>>>>>
>>>>> Isn't this needed for the rootfs on SATA devices?
>>>>
>>>> there's no known boards with rootfs on SATA. Until then, we can reduce
>>>> the size.
>>>
>>> What makes you say so?
>>> The decision for rootfs on SATA is taken dynamically.
>>> OMAP5 boards (specifically cm-t54) can have rootfs on SATA...
>>
>> I'll leave the decision to Tony. Even though they _can_, they really
>> don't and IIRC, OMAP5's SATA has so many silicon errata that it'd be
>> annoying to find that special device which works (e.g it can't negotiate
>> lower speeds with SATA III devices and it won't support SATA I).

Yet, it is not that buggy and at least until now, I di not get any
reports about badly working SATA from customers...

>>
>> As of today, we don't know of anybody really shipping anything with
>> rootfs on SATA and distros would rather ship initiramfs than a giant
>> zImage anyway.

So, you just continue to ignore what I'm saying... even after I point
to a device...

Is it SATA that makes it so giant?
Because I find it worth having in SATA than spare some more k's...

>>
>> Tony, your call.
> 
> I think we should move omap2plus_defconfig to be mostly modular and
> usable for distros as a base. Most distros prefer to build almost
> everything as loadable modules. And my preference is that we should
> only keep the minimum rootfs for devices and serial support as
> built-in and rely on initramfs for most drivers. And slowly move
> also the remaining built-in drivers to be loadable modules.
> 
> The reasons for having drivers as loadable modules are many. It
> allows distros to use the same kernel for all the devices without
> bloating the kernel. It makes developing drivers easier as just the
> module needs to be reloaded. And loadable modules protect us from
> cross-framework spaghetti calls in the kernel as the interfaces are 
> clearly defined.
> 
> Are there people really using SATA as rootfs right now on omaps?

Yes. That is exactly my point.

> 
> If it's only something that will be more widely used in the future,
> then I suggest we make it into a loadable module, and presume
> initramfs and loadable module also for any new devices. The same
> way x86 has been doing with distros for years.

The difference from x86 is that we're in embedded here and
although initramfs is a kind of option, but it means, you need to
load even more data during the boot process... it is annoying and
I would not want to use it on embedded.
(BTW, x86_64_defconfig has it compiled in...)

We can also, split the defconfig as it was some time ago... but I
would not want to go that direction...

If we go the initramfs way, then why not also load MMC from it?
That will also reduce kernel size... (but add initramfs size)

I'm sure you will find making the MMC a loadable module inconvenient.
That how I find making the SATA a loadable module...

Right now, we tell our customers that they can use mainline with
omap2plus_defconfig.
If you decide to drop SATA, we will not be able to do that anymore.

Anyway, like Felipe said, it is your call.
I will not interfere anymore...

-- 
Regards,
Igor.