Re: [PATCH 3/4] lib: logic_pio: Introduce MMIO_LOWER_RESERVED

From: Jiaxun Yang <jiaxun.yang@flygoat.com>
To: John Garry <john.garry@huawei.com>, linux-mips@vger.kernel.org
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Huacai Chen <chenhc@lemote.com>,
	Paul Burton <paulburton@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Stephen Kitt <steve@sk2.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Serge Semin <fancer.lancer@gmail.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Daniel Silsby <dansilsby@gmail.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Paul Cercueil <paul@crapouillou.net>,
	Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Allison Randal <allison@lohutok.net>,
	Tiezhu Yang <yangtiezhu@loongson.cn>,
	Wei Xu <xuwei5@hisilicon.com>,
	linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Linuxarm <linuxarm@huawei.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Rob Herring <robh@kernel.org>
Subject: Re: [PATCH 3/4] lib: logic_pio: Introduce MMIO_LOWER_RESERVED
Date: Mon, 27 Apr 2020 19:03:40 +0800	[thread overview]
Message-ID: <42432F7C-D859-48B4-9547-A61BD22EFEEF@flygoat.com> (raw)
In-Reply-To: <e84f4146-b44f-b009-0dc4-876aa551f44f@huawei.com>

于 2020年4月27日 GMT+08:00 下午6:43:09, John Garry <john.garry@huawei.com> 写到:
>On 26/04/2020 12:47, Jiaxun Yang wrote:
>> That would allow platforms reserve some lower address in PIO MMIO range
>> to deal with legacy drivers with hardcoded I/O ports that can't be
>> managed by logic_pio.
>
>Hi,
>
>Is there some reason why the logic_pio code cannot be improved to handle 
>these devices at these "fixed" addresses? Or do you have a plan to 
>improve it? We already support fixed bus address devices in the INDIRECT 
>IO region.

Hi,

The issue about "Fixed Address" is we can't control the ioport
That driver used to operate devices.
So any attempt to resolve it in logic_pio seems impossible.

Currently we have i8259, i8042, piix4_smbus, mc146818 rely on this assumption.

My plan is after getting this part merged, I'm going to work on a ISA Host bridge driver,
then convert device drivers into logic_pio and Devicetree based driver step by step.

Finally when we nologner have any legacy driver, we can safely remove this reserved
range.

Thanks.

>
>Carving out a region of IO space is less than ideal.
>
>Thanks,
>John
>
>> 
>> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
>> ---
>>   lib/logic_pio.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>> 
>> diff --git a/lib/logic_pio.c b/lib/logic_pio.c
>> index f511a99bb389..57fff1cb7063 100644
>> --- a/lib/logic_pio.c
>> +++ b/lib/logic_pio.c
>> @@ -20,6 +20,10 @@
>>   static LIST_HEAD(io_range_list);
>>   static DEFINE_MUTEX(io_range_mutex);
>>   
>> +#ifndef MMIO_LOWER_RESERVED
>> +#define MMIO_LOWER_RESERVED	0
>> +#endif
>> +
>>   /* Consider a kernel general helper for this */
>>   #define in_range(b, first, len)        ((b) >= (first) && (b) < (first) + (len))
>>   
>> @@ -36,7 +40,7 @@ int logic_pio_register_range(struct logic_pio_hwaddr *new_range)
>>   	struct logic_pio_hwaddr *range;
>>   	resource_size_t start;
>>   	resource_size_t end;
>> -	resource_size_t mmio_end = 0;
>> +	resource_size_t mmio_end = MMIO_LOWER_RESERVED;
>>   	resource_size_t iio_sz = MMIO_UPPER_LIMIT;
>>   	int ret = 0;
>>   
>> 
>

-- 
Jiaxun Yang