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    SubjectRe: [PATCH v4 3/5] drm: add SimpleDRM driver
    On Mon, Aug 22, 2016 at 3:25 PM, Noralf Trønnes <noralf@tronnes.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@gmail.com
    > Cc: libv@skynet.be
    > Signed-off-by: Noralf Trønnes <noralf@tronnes.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.

    > +
    > + 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.

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

    Rob

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