linux-kernel - Re: [PATCH] mmc: Move the mmc driver init earlier

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Date:   Tue, 12 Jun 2018 20:05:25 +0800
From:   Shawn Lin <shawn.lin@...k-chips.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Feng Tang <feng.tang@...el.com>, shawn.lin@...k-chips.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] mmc: Move the mmc driver init earlier

On 2018/6/12 18:29, Ulf Hansson wrote:
> On 12 June 2018 at 10:42, Feng Tang <feng.tang@...el.com> wrote:
>> Hi Ulf,
>>
>> Thanks for the review.
>>
>> On Tue, Jun 12, 2018 at 08:25:44AM +0200, Ulf Hansson wrote:
>>> On 8 June 2018 at 11:51, Feng Tang <feng.tang@...el.com> wrote:
>>>> When doing some boot time optimization for an eMMC rootfs NUCs,
>>>> we found the rootfs may spend around 100 microseconds waiting
>>>> for eMMC card to be initialized, then the rootfs could be
>>>> mounted.
>>>>          [    1.216561] Waiting for root device /dev/mmcblk1p1...
>>>>          [    1.289262] mmc1: new HS400 MMC card at address 0001
>>>>          [    1.289667] mmcblk1: mmc1:0001 R1J56L 14.7 GiB
>>>>          [    1.289772] mmcblk1boot0: mmc1:0001 R1J56L partition 1 8.00 MiB
>>>>          [    1.289869] mmcblk1boot1: mmc1:0001 R1J56L partition 2 8.00 MiB
>>>>          [    1.289967] mmcblk1rpmb: mmc1:0001 R1J56L partition 3 4.00 MiB
>>>>          [    1.292798]  mmcblk1: p1 p2 p3
>>>>          [    1.300576] EXT4-fs (mmcblk1p1): couldn't mount as ext3 due to feature incompatibilities
>>>>          [    1.300912] EXT4-fs (mmcblk1p1): couldn't mount as ext2 due to feature incompatibilities
>>>>
>>>> And this is a common problem for smartphones, tablets, embedded
>>>> devices and automotive products. This patch will make the eMMC/SD
>>>> card  start initializing earlier, by changing its order in drivers/Makefile.
>>>>
>>>> On our platform, the waiting for eMMC card is almost eliminated with the patch,
>>>> which is critical to boot time.
>>>
>>> I am wondering what kernel version you are running here. There have
>>> been some changes to the mmc initialization path, which perhaps can
>>> help.
>> These logs in commit msg are based on kernel 4.14, and the patch is generated
>> against kernel 4.17.
> 
> Right. So it's quite recent, even if lot's of changes have been made
> to the mmc core since then.
> 
> A few things (old/new) that is important.
> 1) Check if your mmc host driver support MMC_CAP_WAIT_WHILE_BUSY. That
> should have some effect, avoiding unnecessary polling.
> 
> 2) Since 4.18 rc1, you will be able to configure an over estimated
> "power on" delay (via DT as well). Look at commit
> 6d796c68cd15234a33a4bd2ef7231125fea2dc6c.

Sorry to chime in. We could also reduce the "power on" delay via hosts'
->set_ios() callback.

> 
> 3) If you use a DT based platform, I think what people do is to
> re-organize the order of device nodes, such that as many as possible
> -EPROBE_DEFER is avoided to be returned by drivers. This is also not a
> good solution, but the best we have at this moment.

Also DT based platform is allowed to add no-sd and no-sdio for the eMMC
node, which could slighly help reduce the boot time.
You could refer to Documentation/devicetree/bindings/mmc/mmc.txt for
details.

> 
>>
>>>
>>>>
>>>> Signed-off-by: Feng Tang <feng.tang@...el.com>
>>>> ---
>>>>   drivers/Makefile | 4 +++-
>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/Makefile b/drivers/Makefile
>>>> index 24cd47014657..c473afd3c688 100644
>>>> --- a/drivers/Makefile
>>>> +++ b/drivers/Makefile
>>>> @@ -50,6 +50,9 @@ obj-$(CONFIG_REGULATOR)               += regulator/
>>>>   # reset controllers early, since gpu drivers might rely on them to initialize
>>>>   obj-$(CONFIG_RESET_CONTROLLER) += reset/
>>>>
>>>> +# put mmc early as many morden devices use emm/sd card as rootfs storage
>>>> +obj-y                          += mmc/
>>>> +
>>>
>>> Your suggested approach isn't really a solution, as it may work for
>>> your particular case but not for everybody else.
>>
>> Do you mean the patch may break some platforms? Yes, I only tested on
>> some IA based NUCs, and I did think about other architectures, things
>> that may affect MMC are gpio/clk/pinctrl, and those are still earlier
>> than mmc after change.
> 
> I don't know if it breaks things, potentially it could, if drivers
> don't implement support for -EPROBE_DEFER properly.
> 
> However, more importantly, it's not real fix to the problem, just
> something that seems to work for you.
> 
> Kind regards
> Uffe
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> 
> 
> 


-- 
Best Regards
Shawn Lin