linux-kernel - Re: [PATCH] mtd: rawnand: omap2: Actually prevent invalid configuration and build error

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Date:   Mon, 7 Mar 2022 23:05:47 +0200
From:   Roger Quadros <rogerq@...nel.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>,
        krzysztof.kozlowski@...onical.com, vigneshr@...com, nm@...com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: rawnand: omap2: Actually prevent invalid
 configuration and build error

Hi Miquel,

On 07/03/2022 16:12, Miquel Raynal wrote:
> Hi Roger,
> 
> rogerq@...nel.org wrote on Mon, 7 Mar 2022 14:25:48 +0200:
> 
>> Hi Miquel,
>>
>> On 07/03/2022 12:03, Miquel Raynal wrote:
>>> Hi Roger,
>>>
>>> rogerq@...nel.org wrote on Sat, 5 Mar 2022 00:50:14 +0200:
>>>   
>>>> Hi Miquel,
>>>>
>>>> On 04/03/2022 17:54, Miquel Raynal wrote:  
>>>>> Hi Guenter, Roger,
>>>>>
>>>>> rdunlap@...radead.org wrote on Sat, 26 Feb 2022 22:55:28 -0800:
>>>>>     
>>>>>> On 2/19/22 16:44, Guenter Roeck wrote:    
>>>>>>> On Sat, Feb 19, 2022 at 09:36:00PM +0200, Roger Quadros wrote:      
>>>>>>>> The root of the problem is that we are selecting symbols that have
>>>>>>>> dependencies. This can cause random configurations that can fail.
>>>>>>>> The cleanest solution is to avoid using select.
>>>>>>>>
>>>>>>>> This driver uses interfaces from the OMAP_GPMC driver so we have to
>>>>>>>> depend on it instead.
>>>>>>>>
>>>>>>>> Fixes: 4cd335dae3cf ("mtd: rawnand: omap2: Prevent invalid configuration and build error")
>>>>>>>> Signed-off-by: Roger Quadros <rogerq@...nel.org>      
>>>>>>>
>>>>>>> Tested-by: Guenter Roeck <linux@...ck-us.net>      
>>>>>>
>>>>>> Tested-by: Randy Dunlap <rdunlap@...radead.org>    
>>>>>
>>>>> Sorry for noticing that just now, but there is still a problem with
>>>>> this patch: we now always compile-in the OMAP_GPMC driver whenever we
>>>>> need the NAND controller, even though it is not needed. This grows the
>>>>> kernel for no reason.    
>>>>
>>>> Sorry, I did not understand what you meant.
>>>>
>>>> We no longer explicitly enable OMAP_GPMC since we dropped the "select".
>>>> This fixes all build issues that were reported recently.
>>>>
>>>> MTD_NAND_OMAP2 will not be enabled if OMAP_GPMC is not since we added
>>>> the "depends on". This fixes the original build issue that we started to
>>>> fix with select initially.  
>>>
>>> Yes, this side is fine.
>>>
>>> In the initial commit, you proposed:
>>>
>>> --- a/drivers/mtd/nand/raw/Kconfig
>>> +++ b/drivers/mtd/nand/raw/Kconfig
>>> @@ -42,7 +42,8 @@ config MTD_NAND_OMAP2
>>>         tristate "OMAP2, OMAP3, OMAP4 and Keystone NAND controller"
>>>         depends on ARCH_OMAP2PLUS || ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
>>>         depends on HAS_IOMEM
>>> +       select OMAP_GPMC if ARCH_K3
>>>
>>> Which creates a dependency over OMAP_GPMC only for a single
>>> architecture. Which means that other OMAP platforms do not necessarily
>>> need OMAP_GPMC for the NAND controller to work. Now, you propose:  
>>
>> No that is not true. Other platforms that need MTD_NAND_OMAP2 are
>> explicitly selecting OMAP_GPMC
>> i.e. in arch/arm/mach-omap2/Kconfig
> 
> Okay, in this case the fix is fine but we will need to clean this up in
> a second time.

What clean up are you implying here? Those legacy platform might need
OMAP_GPMC for booting so they select it. There is nothing much we can do there.

What is left to do now is make user/defconfig files to enable OMAP_GPMC driver
so other platforms that don't need OMAP_GPMC for basic operation can still
enable them later via defconfig or manually by user.

> 
>>> --- a/drivers/mtd/nand/raw/Kconfig
>>> +++ b/drivers/mtd/nand/raw/Kconfig
>>> @@ -42,8 +42,7 @@ config MTD_NAND_OMAP2
>>>  	tristate "OMAP2, OMAP3, OMAP4 and Keystone NAND controller"
>>>  	depends on ARCH_OMAP2PLUS || ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
>>>  	depends on HAS_IOMEM
>>> 	depends on OMAP_GPMC
>>>
>>> This means any of the other OMAP architectures will compile the GPMC
>>> driver even though they might not need it, which would unnecessarily
>>> increase the kernel size.
>>>
>>> Am I missing something?  
>>
>> MTD_NAND_OMAP2 NAND controller is a submodule of the OMAP GPMC IP. So it
>> cannot work without OMAP_GPMC driver.
> 
> I didn't remember exactly but in that case it's okay, I was just
> surprised by the "select GPMC if ARCH_K3" but indeed with this
> explanation it makes more sense.
> 
>> Hope this clarifies the doubts.
> 
> Yes, thanks. I will send the fix to Linus then.
> 
> Cheers,
> Miquèl

cheers,
-roger