linux-kernel - Re: [PATCH v3] USB: Extend usb_device_speed with new value USB_SPEED_SUPER_PLUS

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Message-ID: <20230901215625.lzazscyhkmb4ggdi@synopsys.com>
Date:   Fri, 1 Sep 2023 21:56:33 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     "07c821ae-2391-474c-aec9-65f47d3fecf2@...land.harvard.edu" 
        <07c821ae-2391-474c-aec9-65f47d3fecf2@...land.harvard.edu>
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Subject: Re: [PATCH v3] USB: Extend usb_device_speed with new value
 USB_SPEED_SUPER_PLUS_BY2

Hi,

Please Cc me for changes related to dwc3.

On Sat, Sep 02, 2023, Dingyan Li wrote:
> Currently there are there major generations when speaking of
> USB_SPEED_SUPER_PLUS devices. However, they actually stands
> for different physical speeds. GEN_2x2 means 20Gbps, while
> the others mean 10Gbps. So in order to confirm 20Gbps, both
> speed and generation need ti be checked. This causes a trouble
> for ioctl USBDEVFS_GET_SPEED since it can only return speed
> value to userspace.
> 
> In order not to add a new ioctl to get ssp generation, extending
> usb_device_speed is a good option. The side effect is that
> USB_SPEED_SUPER_PLUS has been used in lots of places and
> it also takes some effort to go through all of them and check
> whether the new speed should be used too.
> 
> Besides, as suggested by Alen, ssp_rate is not a proper name,
> change it to ssp_gen. And change all functions/struct fileds
> ended with ssp_rate to ssp_gen. And there is also some code
> refactor to reduce duplicate definition of strings and increase
> the utilization of commonly defined utilities.
> 
> Signed-off-by: Dingyan Li <18500469033@....com>

Why not spell out the whole thing instead of USB_SPEED_SUPER_PLUS_BY2
(ie. USB_SPEED_SUPER_PLUS_GEN_2x2) as you intended instead of just the
lane count.

There are SuperSpeed Plus generation _and_ lane count. That's why I
didn't name "usb_ssp_gen" that only reflects the generation and not the
lane count. Also, I didn't extend usb_device_speed because gen XxY are
all a single speed: SuperSpeed Plus.

If you're planning to do it this way, why not add the other speeds (such
as gen 1x2) to usb_device_speed enum too? Then we can drop the
usb_ssp_rate enum. If we're going to check multiple enum for SuperSpeed
Plus, we probably need a usb_device_is_superspeed_plus() function.

Now we need to audit all the greater/lesser speed checks that use < or >
to make sure that they are used how they were intended to.

Since these changes are not simple and will touch on multiple places,
please split this patch out.

Thanks,
Thinh