linux-kernel - Re: [PATCH v4 3/5] drm: add SimpleDRM driver

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Message-ID: <b8f7a377-b7c7-5d51-1c80-b24894cd9f12@tronnes.org>
Date:   Thu, 25 Aug 2016 20:42:09 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Rob Herring <robh@...nel.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        David Herrmann <dh.herrmann@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Luc Verhaegen <libv@...net.be>
Subject: Re: [PATCH v4 3/5] drm: add SimpleDRM driver


Den 25.08.2016 15:09, skrev Rob Herring:
> On Mon, Aug 22, 2016 at 3:25 PM, Noralf Trønnes <noralf@...nnes.org> wrote:
>> The SimpleDRM driver binds to simple-framebuffer devices and provides a
>> DRM/KMS API. It provides only a single CRTC+encoder+connector combination
>> plus one initial mode.
>>
>> Userspace can create dumb-buffers which can be blit into the real
>> framebuffer similar to UDL. No access to the real framebuffer is allowed
>> (compared to earlier version of this driver) to avoid security issues.
>> Furthermore, this way we can support arbitrary modes as long as we have a
>> conversion-helper.
>>
>> The driver was originally written by David Herrmann in 2014.
>> My main contribution is to make use of drm_simple_kms_helper and
>> rework the probe path to avoid use of the deprecated drm_platform_init()
>> and drm_driver.{load,unload}().
>> Additions have also been made for later changes to the Device Tree binding
>> document, like support for clocks, regulators and having the node under
>> /chosen. This code was lifted verbatim from simplefb.c.
>>
>> Cc: dh.herrmann@...il.com
>> Cc: libv@...net.be
>> Signed-off-by: Noralf Trønnes <noralf@...nnes.org>
> [...]
>
>> +       /* Count the number of regulator supplies */
>> +       for_each_property_of_node(np, prop) {
>> +               p = strstr(prop->name, SUPPLY_SUFFIX);
>> +               if (p && p != prop->name)
>> +                       count++;
>> +       }
> The regulator API should have functions for this rather than open coding it.

I couldn't find anything that matches this usecase. There are regulator
bulk functions, but they require the names to be known in advance.
And I don't know how many regulators there are nor their names.

>From Documentation/devicetree/bindings/display/simple-framebuffer.txt:

- *-supply : Any number of regulators used by the framebuffer. These should
          be named according to the names in the device's design.

>> +
>> +       if (!count)
>> +               return 0;
>> +
>> +       sdrm->regulators = devm_kcalloc(&pdev->dev, count,
>> +                                       sizeof(struct regulator *),
>> +                                       GFP_KERNEL);
>> +       if (!sdrm->regulators)
>> +               return -ENOMEM;
>> +
>> +       /* Get all the regulators */
>> +       for_each_property_of_node(np, prop) {
>> +               char name[32]; /* 32 is max size of property name */
>> +
>> +               p = strstr(prop->name, SUPPLY_SUFFIX);
>> +               if (!p || p == prop->name)
>> +                       continue;
> This too.
>
>> +
>> +               strlcpy(name, prop->name,
>> +                       strlen(prop->name) - strlen(SUPPLY_SUFFIX) + 1);
>> +               regulator = devm_regulator_get_optional(&pdev->dev, name);
> [...]
>
>> +       if (IS_ENABLED(CONFIG_OF_ADDRESS) && of_chosen) {
>> +               struct device_node *np;
>> +
>> +               for_each_child_of_node(of_chosen, np) {
>> +                       if (of_device_is_compatible(np, "simple-framebuffer"))
> Rather than exporting of_chosen, this whole chunk can be replaced with
> a of_find_compatible_node call. Yes, that would match if
> simple-framebuffer exists somewhere else in the DT, but it is not the
> kernel's job to do DT validation.

This seems to do the job:

     /*
      * The binding doc states that simplefb nodes should be sub-nodes of
      * chosen and that older devicetree files can have them in a different
      * place. of_platform_device_create() just returns NULL if a device
      * has already been created for the node.
      */
     for_each_compatible_node(np, NULL, "simple-framebuffer")
         of_platform_device_create(np, NULL, NULL);


Noralf.

>> +                               of_platform_device_create(np, NULL, NULL);
>> +               }
>> +       }
> Rob
>