Re: [Xen-devel] [RFC 26/29] xen/arm: Add Exynos 4210 UART support for early printk

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On 30/04/13 10:53, Ian Campbell wrote:
> On Mon, 2013-04-29 at 00:02 +0100, Julien Grall wrote:
>> ---
>>  config/arm32.mk                    |    1 +
>>  xen/arch/arm/Rules.mk              |    4 ++
>>  xen/arch/arm/arm32/Makefile        |    1 +
>>  xen/arch/arm/arm32/debug-exynos5.S |   81 
>> ++++++++++++++++++++++++++++++++++++
>>  4 files changed, 87 insertions(+)
>>  create mode 100644 xen/arch/arm/arm32/debug-exynos5.S
>>
>> diff --git a/config/arm32.mk b/config/arm32.mk
>> index 593a1d1..01c1490 100644
>> --- a/config/arm32.mk
>> +++ b/config/arm32.mk
>> @@ -17,6 +17,7 @@ CFLAGS += -marm
>>  # Possible value:
>>  #   - none: no early printk
>>  #   - pl011: printk with PL011 UART
>> +#   - exynos5: printk with the second exynos 5 UART
> 
> From the subject I infer that this UART is an Exynos 4210? If so I think
> that is the correct name to use here, consistent with the pl011 name
> above. (the alternative is that the pl011 is wrong...).
> 
> I suppose in principal a single driver might apply to multiple platforms
> but with different base addresses, but that at build time you need to
> choose a specific platform, which implies a particular driver. The
> current infrastructure doesn't really express that notion.
> 
> What about if we support a mutually exclusive (enforced only by the
> clash of symbols at link time) set of:
>       CONFIG_EARLY_UART_PL011
>       CONFIG_EARLY_UART_EXYNOS4210
> which if defined must be set to the physical address of the port?
> 
> This would mean users need to know the address of the UART on their
> platform rather than just being able to name the platform though.
> Perhaps that's a feature not a bug (i.e. they can choose which UART of
> multiple UARTs if they want). I suppose we could also support
> CONFIG_EARY_UART_PLATFORM=foo and translate into the above.
> 
> Or are there other hardcoded parameters (e.g. crystal rate) which stop
> this?
> 

This drivers have been written with the Exynos 5 platform in mind, so
I'm not sure it can be called exynos4210. There would be few differences
that I can extract from Linux source code, the physical address is
different and the few bit to use FIFO are also different but it's not
use here in the early printk. And I'm almost sure the clock stuff would
be different on an exynos4.

So, in my humble opinion, we should use exynos5 or exynos5250.


>> +/* Exynos 5 UART initialization
>> + * r11: UART base address
>> + * Clobber r0-r1 */
>> +.globl early_uart_init
>> +early_uart_init:
>> +        /* init clock */
>> +        ldr   r1, =0x10020000
>> +        /* select MPLL (800MHz) source clock */
>> +        ldr   r0, [r1, #0x250]
>> +        and   r0, r0, #(~(0xf<<8))
>> +        orr   r0, r0, #(0x6<<8)
>> +        str   r0, [r1, #0x250]
>> +        /* ration 800/(7+1) */
> 
> What does "ration" mean here? It doesn't seem to correspond to the
> French for denominator, numerator, remainder or ratio (at least not
> according to Google Translate ;-))

It mean there is a typo ;), someone or something add a N. I suspect it's
something (the keyboard) :).


-- 
Anthony PERARD

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