linux-kernel - Re: [PATCH v5 2/2] drm/tiny: add driver for Apple Touch Bars in x86 Macs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID:
 <PN3PR01MB9597287D0FFDBD11CC1F6167B8C32@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Tue, 25 Feb 2025 14:54:28 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: Thomas Zimmermann <tzimmermann@...e.de>
CC: "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
	"maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
	"mripard@...nel.org" <mripard@...nel.org>, "airlied@...il.com"
	<airlied@...il.com>, "simona@...ll.ch" <simona@...ll.ch>, Kerem Karabay
	<kekrby@...il.com>, Atharva Tiwari <evepolonium@...il.com>, Aun-Ali Zaidi
	<admin@...eit.net>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 2/2] drm/tiny: add driver for Apple Touch Bars in x86
 Macs



> On 25 Feb 2025, at 5:28 PM, Thomas Zimmermann <tzimmermann@...e.de> wrote:
> 
> Hi
> 
>> Am 25.02.25 um 11:33 schrieb andriy.shevchenko@...ux.intel.com:
>>> On Tue, Feb 25, 2025 at 10:09:42AM +0000, Aditya Garg wrote:
>>> From: Kerem Karabay <kekrby@...il.com>
>>> 
>>> The Touch Bars found on x86 Macs support two USB configurations: one
>>> where the device presents itself as a HID keyboard and can display
>>> predefined sets of keys, and one where the operating system has full
>>> control over what is displayed.
>>> 
>>> This commit adds support for the display functionality of the second
>>> configuration. Functionality for the first configuration has been
>>> merged in the HID tree.
>>> 
>>> Note that this driver has only been tested on T2 Macs, and only includes
>>> the USB device ID for these devices. Testing on T1 Macs would be
>>> appreciated.
>>> 
>>> Credit goes to Ben (Bingxing) Wang on GitHub for reverse engineering
>>> most of the protocol.
>>> 
>>> Also, as requested by Andy, I would like to clarify the use of __packed
>>> structs in this driver:
>>> 
>>> - All the packed structs are aligned except for appletbdrm_msg_information.
>>> - We have to pack appletbdrm_msg_information since it is requirement of
>>>   the protocol.
>>> - We compared binaries compiled by keeping the rest structs __packed and
>>>   not __packed using bloat-o-meter, and __packed was not affecting code
>>>   generation.
>>> - To maintain consistency, rest structs have been kept __packed.
>>> 
>>> I would also like to point out that since the driver was reverse-engineered
>>> the actual data types of the protocol might be different, including, but
>>> not limited to, endianness.
>> ...
>> 
>>> +static int appletbdrm_probe(struct usb_interface *intf,
>>> +                const struct usb_device_id *id)
>>> +{
>>> +    struct usb_endpoint_descriptor *bulk_in, *bulk_out;
>>> +    struct device *dev = &intf->dev;
>>> +    struct appletbdrm_device *adev;
>>> +    struct drm_device *drm;
>>> +    int ret;
>>> +
>>> +    ret = usb_find_common_endpoints(intf->cur_altsetting, &bulk_in, &bulk_out, NULL, NULL);
>>> +    if (ret) {
>>> +        drm_err(drm, "Failed to find bulk endpoints\n");
>> This is simply wrong (and in this case even lead to crash in some circumstances).
>> drm_err() may not be used here. That's my point in previous discussions.
>> Independently on the subsystem the ->probe() for the sake of consistency and
>> being informative should only rely on struct device *dev,
> 
> That's never going to work with DRM. There's so much code in a DRM probe function that uses the DRM error functions.
> 
> This specific instance here is wrong, as the drm pointer hasn't been initialized. But as soon as it is, it's much better to use drm_err() and friends. It will do the right thing and give consistent output across drivers.
> 
Ok so this is actually an interesting case, since I am trying to fix it. To initialise the drm pointer, we need to initialise adev, and to initialise adev, we need to run usb_find_common_endpoints first. So IMO, we cannot use drm_err here, but rather dev_err_probe can be used.
> 
> 
>> 
>>> +        return ret;
>>> +    }
>>> +
>>> +    adev = devm_drm_dev_alloc(dev, &appletbdrm_drm_driver, struct appletbdrm_device, drm);
>>> +    if (IS_ERR(adev))
>>> +        return PTR_ERR(adev);
>>> +
>>> +    adev->in_ep = bulk_in->bEndpointAddress;
>>> +    adev->out_ep = bulk_out->bEndpointAddress;
>>> +    adev->dmadev = dev;
>>> +
>>> +    drm = &adev->drm;
>>> +
>>> +    usb_set_intfdata(intf, adev);
>>> +
>>> +    ret = appletbdrm_get_information(adev);
>>> +    if (ret) {
>>> +        drm_err(drm, "Failed to get display information\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = appletbdrm_signal_readiness(adev);
>>> +    if (ret) {
>>> +        drm_err(drm, "Failed to signal readiness\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = appletbdrm_setup_mode_config(adev);
>>> +    if (ret) {
>>> +        drm_err(drm, "Failed to setup mode config\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = drm_dev_register(drm, 0);
>>> +    if (ret) {
>>> +        drm_err(drm, "Failed to register DRM device\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = appletbdrm_clear_display(adev);
>>> +    if (ret) {
>>> +        drm_err(drm, "Failed to clear display\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
> 
> --
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
>