Re: [PATCH 02/11] omap2/3: Fix DEBUG_LL for omap zoom2/3

[Kevin Hilman <khilman@deeprootsystems.com>]

"Pandita, Vikram" <vikram.pandita@ti.com> writes:

[...]

>>>> > --- a/arch/arm/kernel/head.S
>>>> > +++ b/arch/arm/kernel/head.S
>>>> > @@ -328,6 +328,16 @@ __create_page_tables:
>>>> >  	add	r0, r4, #0xd8000000 >> 18
>>>> >  	str	r3, [r0]
>>>> >  #endif
>>>> > +#if defined(CONFIG_MACH_OMAP_ZOOM2) ||
>>defined(CONFIG_MACH_OMAP_ZOOM3)
>>>> > +	/*
>>>> > +	 * Zoom2 and Zoom3 have UARTs only on the debug board.
>>>> > +	 * The debug board is connected to the GPMC.
>>>> > +	 */
>>>> > +	add	r0, r4, #0xfa000000 >> 18
>>>> > +	orr	r0, r0, #0x00400000 >> 18	@ ZOOM_UART_VIRT
>>>> > +	orr	r3, r7, #0x10000000		@ ZOOM_UART_BASE
>>>> > +	str	r3, [r0]
>>>> > +#endif
>>>>
>>>> I don't see why this part is needed.  The same mapping is done using
>>>> the .io_pg_offset in the machine description which is done just before
>>>> this in head.S
>>>
>>> That mapping does not cover the GPMC area where this UART is.
>>
>>Hmm, then shouldn't that be fixed?  I understood the .phys_io and and
>>.io_pg_offset fields of the mach_desc to be specifically for mapping
>>the early UART, and nothing else.
>
> Here is the problem - with current approach we need two mappings to
> happen and the MACHINE_START() code allows for only one via
> .io_pg_offset and .phys_io
>
> Why:

> Tony's approach is to pass the information about the debug uart
> number from the UART1 Scratchpad register.
>
> this introduces a dependency that 
> UART1 registers also be mapped (virt<->phy).
>
> So for Tony's approach to work, .phys_io/.io_pg_offset continued to
> have 0x4800000 based mapping and for external uart zoom3 port,
> create this extra mapping.
>
> So find a better way from compressed.S to pass the uart number to
> kernel, and we can solve the problem.

Ah, yet another reason to use a memory location instead of UART1 SCR
to pass the UART info (c.f. [1])

Kevin

[1] http://marc.info/?l=linux-omap&m=127266219130713&w=2