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

[Dinh Nguyen <dinguyen@kernel.org>]

On 3/1/19 3:40 AM, Marek Vasut wrote:
> On 3/1/19 12:59 AM, Dinh Nguyen wrote:
>> 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.
> 
> Drat, thanks.
> 
> Better yet, pull the latency config into a function, so it can be used
> by other platforms. The prototype should take 7 parameters, address and
> latency in cycles, so that it shields the users from this n-1 stuff.
> 

Agreed. I'm working on an RFC patch that creates a UBOOT_MISC driver to
handle all of the pl310 settings. Hope to send it out sometime next week.

Dinh