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

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Message-ID: <CACoXjcnpVi6n7__6SgdzYUuMuRkdtZpVGkOiEowFsL8Gq2kC7w@mail.gmail.com>
Date:	Wed, 9 May 2012 10:57:51 +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 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?

>> +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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