linux-kernel - Re: [PATCH v2 14/18] serial: intel: Add CCF support

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Message-ID: <3360edd2-f3d8-b860-13fa-ce680edbfd0a@hauke-m.de>
Date:   Sat, 4 Aug 2018 12:54:22 +0200
From:   Hauke Mehrtens <hauke@...ke-m.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Wu, Songjun" <songjun.wu@...ux.intel.com>
Cc:     hua.ma@...ux.intel.com, yixin.zhu@...ux.intel.com,
        chuanhua.lei@...ux.intel.com, qi-ming.wu@...el.com,
        linux-mips@...ux-mips.org, linux-clk@...r.kernel.org,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH v2 14/18] serial: intel: Add CCF support

On 08/03/2018 12:30 PM, Greg Kroah-Hartman wrote:
> On Fri, Aug 03, 2018 at 03:33:38PM +0800, Wu, Songjun wrote:
>>
>>
>> On 8/3/2018 1:56 PM, Greg Kroah-Hartman wrote:
>>> On Fri, Aug 03, 2018 at 11:02:33AM +0800, Songjun Wu wrote:
>>>> Previous implementation uses platform-dependent API to get the clock.
>>>> Those functions are not available for other SoC which uses the same IP.
>>>> The CCF (Common Clock Framework) have an abstraction based APIs for
>>>> clock. In future, the platform specific code will be removed when the
>>>> legacy soc use CCF as well.
>>>> Change to use CCF APIs to get clock and rate. So that different SoCs
>>>> can use the same driver.
>>>>
>>>> Signed-off-by: Songjun Wu <songjun.wu@...ux.intel.com>
>>>> ---
>>>>
>>>> Changes in v2: None
>>>>
>>>>   drivers/tty/serial/lantiq.c | 11 +++++++++++
>>>>   1 file changed, 11 insertions(+)
>>>>
>>>> diff --git a/drivers/tty/serial/lantiq.c b/drivers/tty/serial/lantiq.c
>>>> index 36479d66fb7c..35518ab3a80d 100644
>>>> --- a/drivers/tty/serial/lantiq.c
>>>> +++ b/drivers/tty/serial/lantiq.c
>>>> @@ -26,7 +26,9 @@
>>>>   #include <linux/clk.h>
>>>>   #include <linux/gpio.h>
>>>> +#ifdef CONFIG_LANTIQ
>>>>   #include <lantiq_soc.h>
>>>> +#endif
>>> That is never how you do this in Linux, you know better.
>>>
>>> Please go and get this patchset reviewed and signed-off-by from other
>>> internal Intel kernel developers before resending it next time.  It is
>>> their job to find and fix your basic errors like this, not ours.
>> Thank you for your comment.
>> Actually, we have discussed this issue internally.
>> We put the reason why we use "#ifdef CONFIG_LANTIQ" preprocessor in commit
>> message in "[PATCH v2 08/18] serial: intel: Get serial id from dts".
>> Please refer the commit message below.
>>
>> "#ifdef CONFIG_LANTIQ" preprocessor is used because LTQ_EARLY_ASC
>> macro is defined in lantiq_soc.h.
>> lantiq_soc.h is in arch path for legacy product support.
>>
>> arch/mips/include/asm/mach-lantiq/xway/lantiq_soc.h
>>
>> If "#ifdef preprocessor" is changed to
>> "if (IS_ENABLED(CONFIG_LANTIQ))", when CONFIG_LANTIQ is not enabled,
>> code using LTQ_EARLY_ASC is compiled.
>> Compilation will fail for no LTQ_EARLY_ASC defined.
> 
> Sorry, but no.  Why is this one tiny driver/chip somehow more "special"
> than all of the tens of thousands of other devices we support to warrent
> it getting some sort of special exception to do things differently?
> What happens to the next device that wants to do it this way?
> 
> Our coding style and rules are there for a reason, do not violate them
> thinking your device is the only one that matters.
> 
> Do it properly, again, you all know better than this.
> 
> greg k-h
> 
Hi Greg,

The problem is that the Lantiq SoC code in arch/mips/lantiq does not use
the common clock framework, but it uses the clk framework directly. It
defines CONFIG_HAVE_CLK and CONFIG_CLKDEV_LOOKUP, but not
CONFIG_COMMON_CLK. The xRX500 SoC which is being added here is about 2
generations more recent than the VR9/xRX200 SoC which is the latest
which is supported by the code in arch/mips/lantiq. With this new SoC we
switched to the common clock framework. This driver is used by the older
SoC and also by the new ones because this IP core is pretty similar in
all the SoCs.
This patch makes it possible to use it with the legacy lantiq code and
also with the common clock framework. I see multiple options to fix this
problem.

1. The current approach to have it as a compile variant for a) legacy
lantiq arch code without common clock framework and b) support for SoCs
using the common clock framework.
2. Convert the lantiq arch code to the common clock framework. This
would be a good approach, but it need some efforts.
3. Remove the arch/mips/lantiq code. There are still users of this code.
4. Use the old APIs also for the new xRX500 SoC, I do not like this
approach.
5. Move lantiq_soc.h to somewhere in include/linux/ so it is globally
available and provide some better wrapper code.

Hauke



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