[U-Boot] [RESEND PATCH 0/3] arm: Introduce writel/readl_relaxed accessors

[André Przywara]

On 29/04/2019 18:16, Jagan Teki wrote:

Hi,

> On Sun, Feb 10, 2019 at 9:49 PM Andre Przywara <andre.przywara at arm.com> wrote:
>>
>> Hi, this is a resend of what I posted some weeks ago, just adding the
>> missing Signed-off-by: in patch 2/3, as pointed out by Philipp. I used
>> the opportunity to add his Reviewed-by: tags on the first two patches.
>> (Many thanks for that!) The rest is unchanged.
>> -------------------
>>
>> Admittedly this is the long way round to solve some nasty SPL code size
>> problem, but it looked beneficial to others as well, so here we go:
>>
>> arch/arm/include/asm/io.h looks like it's been around since the dawn of
>> time, and was more or less blindly copied from Linux.
>> We don't use and don't need most of the definitions, and mainline Linux
>> got rid of them anyway, so patch 1/3 cleans up this header file to
>> just contain what we need in U-Boot.
>>
>> Patch 2/3 introduces readl/writel_relaxed accessors, which are cheaper,
>> but more importantly save one (barrier) instruction per accessor. This
>> helps to bring down code size, since especially DRAM controller inits in
>> SPLs tend to do a lot of MMIO.
>>
>> Consequently patch 3/3 introduces them in the Allwinner H6 DRAM driver,
>> which reduces the SPL size by a whopping 2KB, due to a twist:
>> The AArch64 exception table needs to be 2KB aligned, but we don't do
>> anything special about it the linker script. So depending on where the
>> code before the vectors ends, we have potentially large padding:
>> At the moment this last address is 0x1824 for the H6, so the vectors can
>> only start at 0x2000. By reducing the code size before the vectors by just
>> (at least) 9 instructions, the vectors start at 0x1800 and we save most of
>> the padding.
>>
>> I understand that the proper solution is to fill the gap before the vectors
>> with code instead of NOPs, but I couldn't find any obvious way doing this
>> in the linker script. If anyone has any idea here, I am all ears.
>>
>> Cheers,
>> Andre.
>>
>> Andre Przywara (3):
>>   arm: clean up asm/io.h
>>   arm: introduce _relaxed MMIO accessors
>>   sunxi: H6: use writel_relaxed for DRAM timing register accesses
> 
> These have build issues with arm32, please send another series.

Thanks for the elaborate error report ;-)

There is commit 6478848d165b63293f7021db9b70ce25a1e1062c, which does
basically the same thing as patch 2/3 in this series and was merged by
Tom already. This causes the double definition.
So just dropping the middle patch from this series should do the trick.

Cheers,
Andre.