linux-kernel - Re: [PATCH v2 1/2] drm/panel: add the orisetech ota5601a

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Date:   Thu, 15 Dec 2022 20:22:01 +0100
From:   Christophe Branchereau <cbranchereau@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     thierry.reding@...il.com, sam@...nborg.org, airlied@...il.com,
        daniel@...ll.ch, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] drm/panel: add the orisetech ota5601a

Hello Linus

On Thu, Dec 15, 2022 at 9:42 AM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> Hi Christophe,
>
> thanks for your patch!
>
> On Wed, Dec 14, 2022 at 12:01 PM Christophe Branchereau
> <cbranchereau@...il.com> wrote:
>
> > Add the orisetech ota5601a ic driver
> >
> > For now it only supports the focaltech gpt3 3" 640x480 ips panel
> > found in the ylm rg300x handheld.
> >
> > Signed-off-by: Christophe Branchereau <cbranchereau@...il.com>
> (...)
> > +config DRM_PANEL_ORISETECH_OTA5601A
> > +       tristate "Orise Technology ota5601a RGB/SPI panel"
> > +       depends on OF && SPI
> > +       depends on BACKLIGHT_CLASS_DEVICE
> > +       select REGMAP_SPI
>
> Nice use of regmap in this driver.
>
> > +static const struct reg_sequence ota5601a_panel_regs[] = {
> > +       { 0xfd, 0x00 },
> > +       { 0x02, 0x00 },
> > +
> > +       { 0x18, 0x00 },
> > +       { 0x34, 0x20 },
> > +
> > +       { 0x0c, 0x01 },
> > +       { 0x0d, 0x48 },
> > +       { 0x0e, 0x48 },
> > +       { 0x0f, 0x48 },
> > +       { 0x07, 0x40 },
> > +       { 0x08, 0x33 },
> > +       { 0x09, 0x3a },
> > +
> > +       { 0x16, 0x01 },
> > +       { 0x19, 0x8d },
> > +       { 0x1a, 0x28 },
> > +       { 0x1c, 0x00 },
> > +
> > +       { 0xfd, 0xc5 },
> > +       { 0x82, 0x0c },
> > +       { 0xa2, 0xb4 },
> > +
> > +       { 0xfd, 0xc4 },
> > +       { 0x82, 0x45 },
> > +
> > +       { 0xfd, 0xc1 },
> > +       { 0x91, 0x02 },
> > +
> > +       { 0xfd, 0xc0 },
> > +       { 0xa1, 0x01 },
> > +       { 0xa2, 0x1f },
> > +       { 0xa3, 0x0b },
> > +       { 0xa4, 0x38 },
> > +       { 0xa5, 0x00 },
> > +       { 0xa6, 0x0a },
> > +       { 0xa7, 0x38 },
> > +       { 0xa8, 0x00 },
> > +       { 0xa9, 0x0a },
> > +       { 0xaa, 0x37 },
> > +
> > +       { 0xfd, 0xce },
> > +       { 0x81, 0x18 },
> > +       { 0x82, 0x43 },
> > +       { 0x83, 0x43 },
> > +       { 0x91, 0x06 },
> > +       { 0x93, 0x38 },
> > +       { 0x94, 0x02 },
> > +       { 0x95, 0x06 },
> > +       { 0x97, 0x38 },
> > +       { 0x98, 0x02 },
> > +       { 0x99, 0x06 },
> > +       { 0x9b, 0x38 },
> > +       { 0x9c, 0x02 },
> > +
> > +       { 0xfd, 0x00 },
> > +};
>
> If these are registers, why is register 0xfd written 7 times with different
> values?

It initiates a page shift

> This is rather a jam table or intializations sequence, so it should be
> names something like that and a comment about undocumented
> registers added probably as well.

Honestly I don't remember how I got the panel specsheet, thought it
was widely available but I can't find it anymore online,
so yes I guess at least documenting what each page does could be good
for future reference

> > +static int ota5601a_enable(struct drm_panel *drm_panel)
> > +{
> > +       struct ota5601a *panel = to_ota5601a(drm_panel);
> > +       int err;
> > +
> > +       err = regmap_write(panel->map, 0x01, 0x01);
>
> Since you know what this register does, what about:
>
> #include <linux/bits.h>
>
> #define OTA5601A_CTL 0x01
> #define OTA5601A_CTL_OFF 0x00
> #define OTA5601A_CTL_ON BIT(0)

I can definitely do that if it improves clarity

> > +static int ota5601a_get_modes(struct drm_panel *drm_panel,
> > +                            struct drm_connector *connector)
> > +{
> > +       struct ota5601a *panel = to_ota5601a(drm_panel);
> > +       const struct ota5601a_panel_info *panel_info = panel->panel_info;
> > +       struct drm_display_mode *mode;
> > +       unsigned int i;
> > +
> > +       for (i = 0; i < panel_info->num_modes; i++) {
> > +               mode = drm_mode_duplicate(connector->dev,
> > +                                         &panel_info->display_modes[i]);
> > +               if (!mode)
> > +                       return -ENOMEM;
> > +
> > +               drm_mode_set_name(mode);
> > +
> > +               mode->type = DRM_MODE_TYPE_DRIVER;
> > +               if (panel_info->num_modes == 1)
>
> But ... you have just added an array that contains 2 elements, you
> KNOW it will not be 1.

I know that for the specific panel supported by this driver there are 2 modes,
however in the future someone could want to add a panel using the same IC,
which could have any number of modes

>
> > +                       mode->type |= DRM_MODE_TYPE_PREFERRED;
>
> I think you should probably set this on the preferred resolution
> anyways, take the one you actually use.
>
> > +static const struct of_device_id ota5601a_of_match[] = {
> > +       { .compatible = "focaltech,gpt3", .data = &gpt3_info },
> > +       { /* sentinel */ }
> > +};
> > +MODULE_DEVICE_TABLE(of, ota5601a_of_match);
>
> Does this mean the display controller is ota5601a and the display
> manufacturer and product is focaltech gpt3? Then it's fine.

Yes

> Overall the driver looks very good, just the above little details.

Ok, will do the v3 next week, holidays etc :)

> Yours,
> Linus Walleij