Re: [PATCH V4 5/6] usb: host: xhci-tegra: Add Tegra234 XHCI support

[Wayne Chang <waynec@nvidia.com>]

On 11/23/22 22:20, Jon Hunter wrote:
> 
> On 22/11/2022 16:07, Greg KH wrote:
>> On Fri, Nov 18, 2022 at 03:40:05PM +0000, Jon Hunter wrote:
>>> From: Sing-Han Chen <singhanc@nvidia.com>
>>>
>>> This change adds Tegra234 XUSB host mode controller support.
>>>
>>> In Tegra234, some of the registers have moved to bar2 space.
>>> The new soc variable has_bar2 indicates the chip with bar2
>>> area. This patch adds new reg helper to let the driver reuse
>>> the same code for those chips with bar2 support.
>>>
>>> Signed-off-by: Sing-Han Chen <singhanc@nvidia.com>
>>> Co-developed-by: Wayne Chang <waynec@nvidia.com>
>>> Signed-off-by: Wayne Chang <waynec@nvidia.com>
>>> Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
>>
>> This is should be much slower with the additional redirection.  Is it
>> noticable on this hardware platform with, and without this change?  Or
>> is the hardware slow enough that it doesn't even show up as a speed
>> decrease?
> Wayne, do we have any inputs on this?
> 
> I know that we have been using this implementation now for some time on 
> the kernels we ship and that would be tested on Tegra210, Tegar186, 
> Tegra194 and Tegra234. So I assume that the performance there is good, 
> but not sure about Tegra124.
> 

Hi Jonathan and Greg,

Thanks for the review.
The implementation is out of the difference in hardware implementation
between old chips and tegra234.

Most of the read/write ops are one-time calls during initialization.
Even the mbox msg are seldom used and thus the redirection should not
cause any noticeable performance drop.


thanks,
Wayne.

> Jon
>