[U-Boot] [PATCH] ARM: socfpga: Configure PL310 latencies

[Dinh Nguyen <dinguyen@kernel.org>]

Hi Marek,

On 2/19/19 4:01 AM, Simon Goldschmidt wrote:
> On Tue, Feb 19, 2019 at 1:44 AM Marek Vasut <marex@denx.de> wrote:
>>
>> Configure the PL310 tag and data latency registers, which slightly
>> improves performance and aligns the behavior with Linux.
>>
>> Signed-off-by: Marek Vasut <marex@denx.de>
>> Cc: Dalon Westergreen <dwesterg@gmail.com>
>> Cc: Dinh Nguyen <dinguyen@kernel.org>
>> ---
>>  arch/arm/mach-socfpga/misc.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/mach-socfpga/misc.c b/arch/arm/mach-socfpga/misc.c
>> index 78fbe28724..1ea4e32c11 100644
>> --- a/arch/arm/mach-socfpga/misc.c
>> +++ b/arch/arm/mach-socfpga/misc.c
>> @@ -62,6 +62,9 @@ void v7_outer_cache_enable(void)
>>         /* Disable the L2 cache */
>>         clrbits_le32(&pl310->pl310_ctrl, L2X0_CTRL_EN);
>>
>> +       writel(0x111, &pl310->pl310_tag_latency_ctrl);
>> +       writel(0x121, &pl310->pl310_data_latency_ctrl);
> 
> Would it make sense to add defines as named constants for this?
> OTOH, in Linux, the values in the devicetree aren't really described,
> either, so:

I was thinking the same, so I'm working on a patch to get these values
from the device tree.

So while I was doing that, I realized that this patch is wrong.

The patch should be like this:

	writel(0x0, &pl310->pl310_tag_latency_ctrl);
	writel(0x010, &pl310->pl310_data_latency_ctrl);

The reason is for the latency values:

000 = 1 cycle of latency, there is no additional latency.
001 = 2 cycles of latency.
010 = 3 cycles of latency.
011 = 4 cycles of latency.
100 = 5 cycles of latency.
101 = 6 cycles of latency.
110 = 7 cycles of latency.
111 = 8 cycles of latency.

So from the values in the device tree, they should be n-1.

It looks like you've already sent the patch to Tom. I'll send a follow
up patch to fix that when it lands.

Dinh