linux-kernel - Re: [PATCH v3] usb: hub: Add quirk to decrease IN-ep poll interval for Microchip USB491x hub

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Message-ID: <39f334d2-abe6-4b4d-a48c-b22a907c6ea6@rowland.harvard.edu>
Date:   Fri, 1 Dec 2023 11:13:53 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Hardik Gajjar <hgajjar@...adit-jv.com>
Cc:     gregkh@...uxfoundation.org, corbet@....net,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        erosca@...adit-jv.com, tj@...nel.org, paulmck@...nel.org,
        Martin.Mueller5@...bosch.com
Subject: Re: [PATCH v3] usb: hub: Add quirk to decrease IN-ep poll interval
 for Microchip USB491x hub

On Fri, Dec 01, 2023 at 03:47:05PM +0100, Hardik Gajjar wrote:
> There is a potential delay in notifying Linux USB drivers of downstream
> USB bus activity when connecting a high-speed or superSpeed device via the
> Microchip USB491x hub. This delay is due to the fixed bInterval value of
> 12 in the silicon of the Microchip USB491x hub.
> 
> Microchip requested to ignore the device descriptor and decrease that
> value to 9 as it was too late to modify that in silicon.
> 
> This patch speeds up the USB enummeration process that helps to pass
> Apple Carplay certifications and improve the User experience when utilizing
> the USB device via Microchip Multihost USB491x Hub.
> 
> A new hub quirk HUB_QUIRK_REDUCE_FRAME_INTR_BINTERVAL speeds up
> the notification process for Microchip USB491x hub by limiting
> the maximum bInterval value to 9.
> 
> Signed-off-by: Hardik Gajjar <hgajjar@...adit-jv.com>
> ---
> changes since version 1:
> 	- Move implementation from config.c and quirk.c to hub.c as this is hub
> 	  specific changes.
> 	- Improve commit message.
> 	- Link to v1 - https://lore.kernel.org/all/20231123081948.58776-1-hgajjar@de.adit-jv.com/
> 
> changes since version 2:
>     - Call usb_set_interface after updating the bInterval to Tell the HCD about modification
> 	- Link to v2 - https://lore.kernel.org/all/20231130084855.119937-1-hgajjar@de.adit-jv.com/
> ---
>  drivers/usb/core/hub.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index b4584a0cd484..b5ac29c5f016 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -47,12 +47,18 @@
>  #define USB_VENDOR_TEXAS_INSTRUMENTS		0x0451
>  #define USB_PRODUCT_TUSB8041_USB3		0x8140
>  #define USB_PRODUCT_TUSB8041_USB2		0x8142
> +#define USB_VENDOR_MICROCHIP			0x0424
> +#define USB_PRODUCT_USB4913			0x4913
> +#define USB_PRODUCT_USB4914			0x4914
> +#define USB_PRODUCT_USB4915			0x4915
>  #define HUB_QUIRK_CHECK_PORT_AUTOSUSPEND	0x01
>  #define HUB_QUIRK_DISABLE_AUTOSUSPEND		0x02
> +#define HUB_QUIRK_REDUCE_FRAME_INTR_BINTERVAL	0x08

Why use 0x08 instead of 0x04?

Alan Stern