linux-kernel - Re: [PATCH v5 1/3] usb: serial: Add MaxLinear/Exar USB to Serial driver

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Message-ID: <20210222161119.0bd70a2b@coco.lan>
Date:   Mon, 22 Feb 2021 16:27:34 +0100
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Manivannan Sadhasivam <mani@...nel.org>,
        gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, patong.mxl@...il.com,
        linus.walleij@...aro.org, angelo.dureghello@...esys.com
Subject: Re: [PATCH v5 1/3] usb: serial: Add MaxLinear/Exar USB to Serial
 driver

Hi Johan,

Em Tue, 26 Jan 2021 17:26:36 +0100
Johan Hovold <johan@...nel.org> escreveu:

> On Tue, Jan 26, 2021 at 09:16:04PM +0530, Manivannan Sadhasivam wrote:
> > On Thu, Jan 21, 2021 at 11:19:24AM +0100, Johan Hovold wrote:  
> > > On Sun, Nov 22, 2020 at 10:38:20PM +0530, Manivannan Sadhasivam wrote:  
> > > > Add support for MaxLinear/Exar USB to Serial converters. This driver
> > > > only supports XR21V141X series but it can be extended to other series
> > > > from Exar as well in future.  
> > > 
> > > There are still a few issues with this driver, but I really don't want
> > > to have to review it again in a couple of months so I've fixed it up
> > > myself this time.
> > > 
> > > The trivial stuff I folded into this patch, and I'll submit a follow-on
> > > series for the rest.
> > >   
> > 
> > Many thanks for doing this! These days it is really difficult to find
> > time for spare time stuffs.
> > 
> > And all of your fixes makes sense to me.  
> 
> Thanks for taking a look!

Thanks for merging it!

-

I'm now facing an issue with this driver. I have here two different
boards with those USB UART from MaxLinear/Exar.

The first one is identical to Mani's one:
	USB_DEVICE(0x04e2, 0x1411)
The second one is a different version of it:
	USB_DEVICE(0x04e2, 0x1424)

By looking at the final driver merged at linux-next, it sounds that
somewhere during the review of this series, it lost the priv struct,
and the xr_probe function. It also lost support for all MaxLinear/Exar
devices, except for just one model (04e2:1411).

The original submission:

	https://lore.kernel.org/linux-usb/20180404070634.nhspvmxcjwfgjkcv@advantechmxl-desktop

And the manufacturer's Linux driver on their website:

	https://www.maxlinear.com/support/design-tools/software-drivers

Had support for other 12 different models of the MaxLinear/Exar USB
UART. 

Those are grouped into 5 different major types:

	+	init_xr2280x_reg_map();
	+	init_xr21b142x_reg_map();
	+	init_xr21b1411_reg_map();
	+	init_xr21v141x_reg_map();
	+
	+	if ((xrusb->DeviceProduct & 0xfff0) == 0x1400)
	+		memcpy(&(xrusb->reg_map), &xr2280x_reg_map,
	+			sizeof(struct reg_addr_map));
	+	else if ((xrusb->DeviceProduct & 0xFFF0) == 0x1420)
	+		memcpy(&(xrusb->reg_map), &xr21b142x_reg_map,
	+			sizeof(struct reg_addr_map));
	+	else if (xrusb->DeviceProduct == 0x1411)
	+		memcpy(&(xrusb->reg_map), &xr21b1411_reg_map,
	+			sizeof(struct reg_addr_map));
	+	else if ((xrusb->DeviceProduct & 0xfff0) == 0x1410)
	+		memcpy(&(xrusb->reg_map), &xr21v141x_reg_map,
	+			sizeof(struct reg_addr_map));
	+	else
	+		rv = -1;

Note: Please don't be confused by "reg_map" name. This has nothing
      to do with Linux regmap API ;-)

What happens is that different USB IDs have different values for
each register. So, for instance, the UART enable register is set to
either one of the following values, depending on the value of
udev->descriptor.idProduct:

	xr21b140x_reg_map.uart_enable_addr = 0x00;
	xr21b1411_reg_map.uart_enable_addr = 0xc00;
	xr21v141x_reg_map.uart_enable_addr = 0x03;
	xr21b142x_reg_map.uart_enable_addr = 0x00;

There are other values that depend on the probing time detection,
based on other USB descriptors. Those set several fields at the
priv data that would allow to properly map the registers.

Also, there are 4 models that support multiple channels. On those,
there are one pair of register get/set for each channel.

-

In summary, while supporting just 04e2:1411 there's no need for
a private struct, in order to properly support the other models,
some autodetection is needed. The best way of doing that is to
re-add the .probe method and adding a priv struct.

As I dunno why this was dropped in the first place, I'm wondering
if it would be ok to re-introduce them.

To be clear: my main focus here is just to avoid needing to use 
Windows in order to use the serial console of the hardware with
the 0x1424 variant ;-)

I can't test the driver with the other hardware, but, IMHO, instead
of adding a hack to support 0x1424, the better (but more painful)
would be to re-add the auto-detection part and support for the
other models.

Thanks!
Mauro