[U-Boot] [PATCH v2 10/10] boston: Introduce support for the MIPS Boston development board

[Paul Burton]

On 31/07/16 16:56, Marek Vasut wrote:
> On 07/29/2016 10:36 AM, Paul Burton wrote:
> [...]
>>>> +#ifndef __ASSEMBLY__
>>>> +
>>>> +#include <asm/io.h>
>>>> +
>>>> +#define BUILD_PLAT_ACCESSORS(offset, name)                \
>>>> +static inline uint32_t read_boston_##name(void)                \
>>>> +{                                    \
>>>> +    uint32_t *reg = (void *)CKSEG1ADDR(BOSTON_PLAT_BASE) + (offset);\
>>>> +    return __raw_readl(reg);                    \
>>>> +}
>>>
>>> Don't we have enough standard accessors to confuse people ?
>>> Why do you add another custom ones ? Remove this and just use
>>> standard accessors throughout the code.
>>
>> Hi Marek,
>>
>> These accessors are simple wrappers around __raw_readl, I'd hardly say
>> they can be considered confusing. The alternative is lots of:
>>
>>     val = __raw_readl((void *)CKSEG1ADDR(BOSTON_PLAT_BASE) + OFFSET);
>>
>> ...and that is just plain ugly.
>
> This should be map_physmem() + readl(), see ie. the ag7xxx.c driver or
> whatever other stuff from the atheros ath79 port. Does this work ?

Yes this works. I suggest you read about the MIPS memory map if you wish 
to critique this code.

>> Invoking readl on a field of a struct
>> representing these registers would be nice, but some of them need to be
>> accessed from assembly so that would involve duplication which isn't
>> nice.
>
> The struct based access is deprecated, don't bother with it.
>
>> I think this way is the best option, where if you want to read the
>> Boston core_cl register you call read_boston_core_cl() - it's hardly
>> confusing what that does.
>
> Now imagine what would happen if everyone introduced his own
> my_platform_read_random_register() accessor(s) . This would be utter chaos.

You speak as though this patch introduces new general purpose accessor 
functions that perform some arbitrary memory read. It does not. It 
introduces functions each of which reads a single register in the only 
sane way to read that register, via the standard __raw_readl. It does so 
in a pretty well namespaced manner & with names that match the register 
names of the platform. If everyone were to do that I fail to see what 
the problem would be.

>>>> +BUILD_PLAT_ACCESSORS(BOSTON_PLAT_CORE_CL, core_cl)
>>>> +BUILD_PLAT_ACCESSORS(BOSTON_PLAT_MMCMDIV, mmcmdiv)
>>>> +BUILD_PLAT_ACCESSORS(BOSTON_PLAT_DDRCONF0, ddrconf0)
>>>> +
>>>> +#endif /* !__ASSEMBLY__ */
>>>> +
>>>> +#endif /* __BOARD_BOSTON_REGS_H__ */
>>>> diff --git a/board/imgtec/boston/checkboard.c
>>>> b/board/imgtec/boston/checkboard.c
>>>> new file mode 100644
>>>> index 0000000..417ac4e
>>>> --- /dev/null
>>>> +++ b/board/imgtec/boston/checkboard.c
>>>> @@ -0,0 +1,29 @@
>>>> +/*
>>>> + * Copyright (C) 2016 Imagination Technologies
>>>> + *
>>>> + * SPDX-License-Identifier:    GPL-2.0
>>>> + */
>>>> +
>>>> +#include <common.h>
>>>> +
>>>> +#include <asm/mipsregs.h>
>>>> +
>>>> +#include "boston-lcd.h"
>>>> +#include "boston-regs.h"
>>>>
>>>> +int checkboard(void)
>>>> +{
>>>> +    u32 changelist;
>>>> +
>>>> +    lowlevel_display("U-boot  ");
>>>> +
>>>> +    printf("Board: MIPS Boston\n");
>>>> +
>>>> +    printf("CPU:   0x%08x", read_c0_prid());
>>>
>>> This should be in print_cpuinfo()
>>
>> I don't agree. This goes on to read a board-specific register to
>> determine information about the CPU (the revision of its RTL) and that
>> should not be done in arch-level code, which is what every other
>> implementation of print_cpuinfo is.
>
> Ah, so the register used to determine CPU info is board-specific ? That
> is utterly braindead design in my mind. The read_c0_prid() looked like
> it is reading some standard register, maybe that's not true ...

read_c0_prid() is generic, it's the read_boston_core_cl() that is 
board-specific & used to print the CPU's RTL revision, as I described 
with "goes on to...". I disagree that this is a bad design. It's pretty 
logical that an FPGA based development platform might wish to expose 
more information about the CPU loaded on it, such as its RTL revision, 
than that CPU would expose in general use.

You can insult the design of the system all you like if it makes you 
feel better. However, if you expect me to pay any attention to your 
opinions then I suggest that you'd do better to make an effort to 
understand the system rather than than spewing insulting words & false 
assertions about memory accesses being broken or branches being 
incorrectly written.

Thanks,
     Paul