linux-kernel - Re: [PATCH 2/2] MIPS: Add custom serial.h with BASE

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Message-ID: <c33143de-4aa1-828c-a5bf-015545c50a93@mips.com>
Date:   Tue, 28 Nov 2017 15:20:08 +0000
From:   Matt Redfearn <matt.redfearn@...s.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
        <linux-serial@...r.kernel.org>, <linux-mips@...ux-mips.org>,
        "stable # 4 . 14" <stable@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Paul Burton <paul.burton@...s.com>,
        Ingo Molnar <mingo@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 2/2] MIPS: Add custom serial.h with BASE_BAUD override for
 generic kernel



On 28/11/17 14:35, Greg Kroah-Hartman wrote:
> On Wed, Nov 22, 2017 at 09:57:29AM +0000, Matt Redfearn wrote:
>> Add a custom serial.h header for MIPS, allowing platforms to override
>> the asm-generic version if required.
>>
>> The generic platform uses this header to set BASE_BAUD to 0. The
>> generic platform supports multiple boards, which may have different
>> UART clocks. Also one of the boards supported is the Boston FPGA board,
>> where the UART clock depends on the loaded FPGA bitfile. As such there
>> is no way that the generic kernel can set a compile time default
>> BASE_BAUD.
>>
>> Commit 31cb9a8575ca ("earlycon: initialise baud field of earlycon device
>> structure") changed the behavior of of_setup_earlycon such that any baud
>> rate set in the device tree is now set in the earlycon structure. The
>> UART driver will then calculate a divisor based on BASE_BAUD and set it.
>> With MIPS generic kernels this resulted in garbage output due to the
>> incorrect uart clock rate being used to calculate a divisor. This
>> commit, combined with "serial: 8250_early: Only set divisor if valid clk
>> & baud" prevents the earlycon code setting a bad divisor and restores
>> earlycon output.
>>
>> Fixes: 31cb9a8575ca ("earlycon: initialise baud field of earlycon device structure")
>> Cc: stable <stable@...r.kernel.org> # 4.14
>> Signed-off-by: Matt Redfearn <matt.redfearn@...s.com>
>>
>> ---
>>
>>   arch/mips/include/asm/Kbuild   |  1 -
>>   arch/mips/include/asm/serial.h | 21 +++++++++++++++++++++
>>   2 files changed, 21 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/mips/include/asm/serial.h
>>
>> diff --git a/arch/mips/include/asm/Kbuild b/arch/mips/include/asm/Kbuild
>> index 7c8aab23bce8..b1f66699677d 100644
>> --- a/arch/mips/include/asm/Kbuild
>> +++ b/arch/mips/include/asm/Kbuild
>> @@ -16,7 +16,6 @@ generic-y += qrwlock.h
>>   generic-y += qspinlock.h
>>   generic-y += sections.h
>>   generic-y += segment.h
>> -generic-y += serial.h
>>   generic-y += trace_clock.h
>>   generic-y += unaligned.h
>>   generic-y += user.h
>> diff --git a/arch/mips/include/asm/serial.h b/arch/mips/include/asm/serial.h
>> new file mode 100644
>> index 000000000000..30be5cd8efdb
>> --- /dev/null
>> +++ b/arch/mips/include/asm/serial.h
>> @@ -0,0 +1,21 @@
>> +/*
>> + * This file is subject to the terms and conditions of the GNU General Public
>> + * License.  See the file "COPYING" in the main directory of this archive
>> + * for more details.
> 
> Which version of the GPL?  As it is, this means "GPL v1 and all others".
> 
> I doubt you want that :)

Good point - thanks!

Matt

> 
> thanks,
> 
> greg k-h
>