linux-kernel - Re: [V2 5/5] powerpc: kernel: 16650 UART reg-shift support

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Date:	Mon, 21 May 2012 09:48:08 +0530
From:	Tanmay Inamdar <tinamdar@....com>
To:	Josh Boyer <jwboyer@...il.com>
Cc:	benh@...nel.crashing.org, grant.likely@...retlab.ca,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [V2 5/5] powerpc: kernel: 16650 UART reg-shift support

On Wed, May 9, 2012 at 10:57 AM, Tanmay Inamdar <tinamdar@....com> wrote:
> On Wed, May 2, 2012 at 7:08 PM, Josh Boyer <jwboyer@...il.com> wrote:
>> On Mon, Apr 9, 2012 at 3:20 AM, Tanmay Inamdar <tinamdar@....com> wrote:
>>> In APM8018X SOC, UART register address space has been relocated to 32-bit
>>> data boundaries for APB bus implementation.
>>> Current legacy_serial driver ignores the reg-shift property. This patch
>>> modifies legacy_serial.c and udbg_16550.c to work with above mentioned UARTs.
>>>
>>> Signed-off-by: Tanmay Inamdar <tinamdar@....com>
>>> ---
>>> :100644 100644 8338aef... f5fc106... M  arch/powerpc/include/asm/udbg.h
>>> :100644 100644 bedd12e... d523b7d... M  arch/powerpc/kernel/legacy_serial.c
>>> :100644 100644 6837f83... e0cb7dc... M  arch/powerpc/kernel/udbg_16550.c
>>>  arch/powerpc/include/asm/udbg.h     |    2 +-
>>>  arch/powerpc/kernel/legacy_serial.c |   16 +++++---
>>>  arch/powerpc/kernel/udbg_16550.c    |   64 ++++++++++++++++++++++------------
>>>  3 files changed, 52 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/udbg.h b/arch/powerpc/include/asm/udbg.h
>>> index 8338aef..f5fc106 100644
>>> --- a/arch/powerpc/include/asm/udbg.h
>>> +++ b/arch/powerpc/include/asm/udbg.h
>>> @@ -29,7 +29,7 @@ extern void udbg_printf(const char *fmt, ...)
>>>  extern void udbg_progress(char *s, unsigned short hex);
>>>
>>>  extern void udbg_init_uart(void __iomem *comport, unsigned int speed,
>>> -                          unsigned int clock);
>>> +                          unsigned int clock,  unsigned int regshift);
>>>  extern unsigned int udbg_probe_uart_speed(void __iomem *comport,
>>>                                          unsigned int clock);
>>>
>>> diff --git a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
>>> index bedd12e..d523b7d 100644
>>> --- a/arch/powerpc/kernel/legacy_serial.c
>>> +++ b/arch/powerpc/kernel/legacy_serial.c
>>> @@ -33,6 +33,7 @@ static struct legacy_serial_info {
>>>        unsigned int                    clock;
>>>        int                             irq_check_parent;
>>>        phys_addr_t                     taddr;
>>> +       unsigned int                    regshift;
>>>  } legacy_serial_infos[MAX_LEGACY_SERIAL_PORTS];
>>>
>>>  static struct __initdata of_device_id legacy_serial_parents[] = {
>>> @@ -42,6 +43,7 @@ static struct __initdata of_device_id legacy_serial_parents[] = {
>>>        {.compatible = "ibm,opb",},
>>>        {.compatible = "simple-bus",},
>>>        {.compatible = "wrs,epld-localbus",},
>>> +       {.compatible = "apm,apb",},
>>>        {},
>>>  };
>>>
>>> @@ -163,11 +165,6 @@ static int __init add_legacy_soc_port(struct device_node *np,
>>>        if (of_get_property(np, "clock-frequency", NULL) == NULL)
>>>                return -1;
>>>
>>> -       /* if reg-shift or offset, don't try to use it */
>>> -       if ((of_get_property(np, "reg-shift", NULL) != NULL) ||
>>> -               (of_get_property(np, "reg-offset", NULL) != NULL))
>>> -               return -1;
>>> -
>>
>> So we explicitly didn't support reg-shift before.  I'm guessing there is
>> a reason for that, but I don't recall what.  Ben?
>>
>> Also, why do you need to use the legacy serial driver at all for this
>> SOC?  As far as I remember, the OF serial driver should be sufficient.
>>
>
> You are right. There is no need to use legacy serial driver. However I
> realized that when 40x is selected, 'PPC_UDBG_16550' is by default
> selected. This enables legacy serial driver.
>
> Is it now required to enable 'PPC_UDBG_16550' by default for every SOC
> that uses 40x processor?
>
Josh, Ben,

Please let me know if you have any comments regarding above question.

>>> +static unsigned int reg_shift;
>>> +#define ns16550_offset(addr) (addr - (unsigned char *)udbg_comport)
>>> +
>>>  static struct NS16550 __iomem *udbg_comport;
>>>
>>> +static inline u8 serial_read(unsigned char *addr)
>>> +{
>>> +       u32 offset = ns16550_offset(addr) << reg_shift;
>>> +       return readb(udbg_comport + offset);
>>> +}
>>> +
>>> +static inline void serial_write(unsigned char *addr, char val)
>>> +{
>>> +       u32 offset = ns16550_offset(addr) << reg_shift;
>>> +       writeb(val, udbg_comport + offset);
>>> +}
>>> +
>>
>> I don't think readb/writeb are correct here.  Why did you switch to
>> using those instead of sticking with in_8/out_8?
>>
>> josh
>
> Thanks,
> Tanmay
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