RE: [PATCH 1/6] USB: serial: ftdi_sio: add configurable inter-batch defer for read URBs

[Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)]

Hi Greg,

On Mon, Jun 22, 2026 at 04:52:00PM +0000, Greg Kroah-Hartman wrote:
> This is not the 1990's, module parameters should not be used anymore...
> Why not just fix this at the root of the problem?

Thank you for the review, Greg.

You are right on both points.

On the module parameter: I will switch to sysfs if the per-driver approach
is accepted, or drop it entirely.

On the location: your core point is well-taken. The DMA channel starvation
is a BCM2835 DWC_OTG host controller deficiency, and the correct fix
belongs in the host controller driver, not in each USB device driver.
I will investigate fixing it there instead. If that is not feasible (the
BCM2835 DWC_OTG is a vendor tree that Broadcom/RPi maintain outside
mainline), I will report back before proposing any per-driver workaround.

I will drop patch 1 from the series for now and resubmit patches 2-6
independently, as those address ftdi_sio-specific issues (latency_timer
reliability, low_latency race, per-port sysfs attribute) that stand on
their own merits.

On the dev_dbg() nit: understood, I will remove __func__ in v2.

Thanks,
Naveen

-----Original Message-----
From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> 
Sent: Monday, 22 June 2026 4:52 pm
To: Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG) <naveen.reddy@xxxxxxxxxxxx>
Cc: Johan Hovold <johan@xxxxxxxxxx>; linux-usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Arun Pappan (FTDI-SG) <arun.pappan@xxxxxxxxxxxx>
Subject: Re: [PATCH 1/6] USB: serial: ftdi_sio: add configurable inter-batch defer for read URBs

On Mon, Jun 22, 2026 at 03:38:34PM +0800, Chinna Mopurigari Naveen Kumar Reddy wrote:
> +		if (res) {
> +			dev_dbg(&port->dev, "%s - submit failed: %d\n",
> +				__func__, res);

Minor nit, dev_dbg() already has the __func__ information in it, never duplicate it again as that's just waste.

thanks,

greg k-h