Re: [PATCH] ARM: multi_v7_defconfig: make USB_DWC3 as a module instead of built-in

From: Roger Quadros <rogerq@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>,
	Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	Russell King <linux@armlinux.org.uk>
Cc: Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
	Nishanth Menon <nm@ti.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Vignesh Raghavendra <vigneshr@ti.com>
Subject: Re: [PATCH] ARM: multi_v7_defconfig: make USB_DWC3 as a module instead of built-in
Date: Tue, 4 Apr 2023 15:59:53 +0300	[thread overview]
Message-ID: <87cc8d92-0345-bc4b-60e8-1ca016691371@kernel.org> (raw)
In-Reply-To: <08b12571-5ca6-4e3d-8c56-5fc48827d17a@app.fastmail.com>

On 04/04/2023 15:14, Arnd Bergmann wrote:
> On Tue, Apr 4, 2023, at 13:46, Roger Quadros wrote:
>> On 04/04/2023 13:01, Krzysztof Kozlowski wrote:
>>> On 04/04/2023 10:51, Arnd Bergmann wrote:
>>>> On Tue, Apr 4, 2023, at 10:42, Roger Quadros wrote:
>>>>> USB_DWC3 is not required for boot on most platforms make it
>>>>> as a module instead of built-in.
>>>>>
>>>>> Signed-off-by: Roger Quadros <rogerq@kernel.org>
>>>>> ---
>>>>
>>>> Does this save a significant amount of vmlinux size? Since this
>>
>> vmlinux size reduces by ~529KB
> 
> That seems really high, so I had a look at what's going on.

It was based on the configuration we are using at TI.

(as built-in)

$ size vmlinux
   text	   data	    bss	    dec	    hex	filename
14616949	5285870	 491776	20394595	1373263	vmlinux
$ ls -l vmlinux
-rwxrwxr-x 1 roger roger 120866544 Apr  4 15:54 vmlinux

(as module)

$ size vmlinux
   text	   data	    bss	    dec	    hex	filename
14550571	5258106	 491776	20300453	135c2a5	vmlinux
$ ls -l vmlinux
-rwxrwxr-x 1 roger roger 120324528 Apr  4 15:52 vmlinux

$ diff built-in-config module-config
5547c5547
< CONFIG_USB_XHCI_PLATFORM=y
---
> CONFIG_USB_XHCI_PLATFORM=m
5614c5614
< CONFIG_USB_DWC3=y
---
> CONFIG_USB_DWC3=m

> 
> Testing this on multi_v7_defconfig with gcc-13, I only see
> 163KB difference in (uncompressed) vmlinux file size, or 140KB
> in the output of 'size vmlinux'. This still seems high, and
> looking more closely I find that a lot of that is for either
> Gadget mode or debugfs, while the driver itself is not all
> that big (most of the host logic is in the xhci driver).
> 
> Turning off gadget mode altogether would save 248KB
> in 'size vmlinux' output, but would also prevent us
> from enabling gadget driver modules, which is not great
> either.
> 
> I tried setting CONFIG_USB_GADGET=m, but that makes
> DWC3 and DWC2 host-only and turns CHIPIDEA into a loadable
> module, so we probably don't want to do that either:
> 
> -CONFIG_USB_EHCI_HCD_OMAP=y
> +CONFIG_USB_EHCI_HCD_OMAP=m
> -CONFIG_USB_DWC3_DUAL_ROLE=y
> +CONFIG_USB_DWC3_HOST=y
> +CONFIG_USB_DWC2_HOST=y
> -CONFIG_USB_DWC2_DUAL_ROLE=y
> -CONFIG_USB_CHIPIDEA=y
> +CONFIG_USB_CHIPIDEA=m
> -CONFIG_USB_ISP1761_UDC=y
> -CONFIG_USB_ISP1760_DUAL_ROLE=y
> +CONFIG_USB_ISP1760_HOST_ROLE=y
> 
>     Arnd

cheers,
-roger

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