Hello Andy,
Thanks for your feedback.
On 2/4/22 15:26, Andy Shevchenko wrote:
> On Fri, Feb 04, 2022 at 02:43:45PM +0100, Javier Martinez Canillas wrote:
>> Add a DRM driver for SSD1305, SSD1306, SSD1307 and SSD1309 Solomon OLED
>> controllers that can be programmed via an I2C interface. This is a port
>> of the ssd1307fb driver that already supports these devices.
>>
>> A Device Tree binding is not added because the DRM driver is compatible
>> with the existing binding for the ssd1307fb driver.
>
> ...
>
>> +/*
>> + * DRM driver for Solomon SSD130X OLED displays
>> + *
>> + * Copyright 2022 Red Hat Inc.
>> + *
>> + * Based on drivers/video/fbdev/ssd1307fb.c
>> + * Copyright 2012 Free Electrons
>
>> + *
>
> No need for this blank line.
>
Ok.
>> + */
>
> ...
>
>> +struct ssd130x_device {
>> + struct drm_device drm;
>> + struct drm_simple_display_pipe pipe;
>> + struct drm_display_mode mode;
>> + struct drm_connector connector;
>
>
>> + struct i2c_client *client;
>
> Can we logically separate hw protocol vs hw interface from day 1, please?
> This will allow to add SPI support for this panel much easier.
>
> Technically I would like to see here
>
> struct device *dev;
>
> and probably (I haven't looked into design)
>
> struct ssd130x_ops *ops;
>
> or something alike.
>
Sure. I wanted to keep the driver simple, making the writes bus agnostic and
adding a level of indirection would make it more complex. But I agree that
it will also make easier to add more buses later. I will do that for v3.
[snip]
>
>> +static inline int ssd130x_write_value(struct i2c_client *client, u8 value)
>
> Not sure inline does anything useful here.
> Ditto for the rest similar cases.
>
Ok, I'll drop them.
> ...
>
>> +static inline int ssd130x_write_cmd(struct i2c_client *client, int count,
>> + /* u8 cmd, u8 value, ... */...)
>> +{
>> + va_list ap;
>> + u8 value;
>> + int ret;
>> +
>> + va_start(ap, count);
>
>> + while (count--) {
>> + value = va_arg(ap, int);
>> + ret = ssd130x_write_value(client, (u8)value);
>> + if (ret)
>> + goto out_end;
>> + }
>
> I'm wondering if this can be written in a form
>
> do {
> ...
> } while (--count);
>
> In this case it will give a hint that count can't be 0.
>
Sure, I don't have a strong preference. I will change it.
[snip]
>> + ssd130x->pwm = pwm_get(dev, NULL);
>> + if (IS_ERR(ssd130x->pwm)) {
>> + dev_err(dev, "Could not get PWM from device tree!\n");
>
> "device tree" is a bit confusing here if I run this on ACPI.
> Maybe something like "firmware description"?
>
Indeed.
>> + return PTR_ERR(ssd130x->pwm);
>> + }
>
> ...
>
>> + /* Set initial contrast */
>> + ret = ssd130x_write_cmd(ssd130x->client, 2, SSD130X_CONTRAST, ssd130x->contrast);
>
> Creating a local variable for client allows to:
> - make lines shorter and might even be less LOCs
> - allow to convert struct device to client in one place
> (as per my above comment)
>
> Ditto for other similar cases.
>
Ok.
[snip]
>> + /* Switch to horizontal addressing mode */
>> + ret = ssd130x_write_cmd(ssd130x->client, 2, SSD130X_SET_ADDRESS_MODE,
>> + SSD130X_SET_ADDRESS_MODE_HORIZONTAL);
>> + if (ret < 0)
>> + return ret;
>> +
>> + return 0;
>
> Can it be
>
> return ssd130x_write_cmd(...);
>
> ?
>
> ...
>
Yes.
>> + unsigned int line_length = DIV_ROUND_UP(width, 8);
>> + unsigned int pages = DIV_ROUND_UP(height, 8);
>
> For power of two there are more efficient roundup()/rounddown()
> (or with _ in the names, I don't remember by heart).
>
Oh, I didn't know about round_{up,down}(). Thanks a lot for the pointer.
> ...
>
>> + for (k = 0; k < m; k++) {
>
>> + u8 byte = buf[(8 * i + k) * line_length +
>> + j / 8];
>
> One line?
>
Yes.
>> + u8 bit = (byte >> (j % 8)) & 1;
>> +
>> + data |= bit << k;
>> + }
>
> ...
>
>> +static int ssd130x_display_pipe_mode_valid(struct drm_simple_display_pipe *pipe,
>> + const struct drm_display_mode *mode)
>> +{
>> + struct ssd130x_device *ssd130x = drm_to_ssd130x(pipe->crtc.dev);
>> +
>> + if (mode->hdisplay != ssd130x->mode.hdisplay &&
>> + mode->vdisplay != ssd130x->mode.vdisplay)
>> + return MODE_ONE_SIZE;
>
>> + else if (mode->hdisplay != ssd130x->mode.hdisplay)
>> + return MODE_ONE_WIDTH;
>> + else if (mode->vdisplay != ssd130x->mode.vdisplay)
>> + return MODE_ONE_HEIGHT;
>
> 'else' in both cases is redundant.
>
Indeed.
>> + return MODE_OK;
>> +}
>
> ...
>
>> +poweroff:
>
> out_power_off: ?
>
Ok.
> ...
>
>> + if (!fb)
>> + return;
>
> Can it happen?
>
I don't know, but saw that the handler of other drivers checked for this so
preferred to play safe and do the same.
> ...
>
>> + drm_mode_probed_add(connector, mode);
>> + drm_set_preferred_mode(connector, mode->hdisplay, mode->vdisplay);
>> +
>> + return 1;
>
> Positive code, what is the meaning of it?
>
It's the number of connector modes. The driver only supports 1.
> ...
>
>> + if (device_property_read_u32(dev, "solomon,prechargep2", &ssd130x->prechargep2))
>> + ssd130x->prechargep2 = 2;
>
> You can drop conditionals for the optional properties
>
> ssd130x->prechargep2 = 2;
> device_property_read_u32(dev, "solomon,prechargep2", &ssd130x->prechargep2);
>
> and so on for the similar.
>
Ok.
> ...
>
>> + ssd130x->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
>> + if (IS_ERR(ssd130x->reset)) {
>
>> + ret = PTR_ERR(ssd130x->reset);
>> + dev_err(dev, "Failed to get reset gpio: %d\n", ret);
>> + return ret;
>
> Why not
>
> return dev_err_probe()?
>
> Each time you call it for deferred probe, it will spam logs.
>
Right. I'll change in all the places you pointed out.
[snip]
> ...
>
>> + {},
>
> Comma is not needed in terminator entry.
>
Right.
> ...
>
>> +static struct i2c_driver ssd130x_i2c_driver = {
>> + .driver = {
>> + .name = DRIVER_NAME,
>> + .of_match_table = ssd130x_of_match,
>> + },
>> + .probe_new = ssd130x_probe,
>> + .remove = ssd130x_remove,
>> + .shutdown = ssd130x_shutdown,
>> +};
>
>> +
>
> Redundant blank line.
>
Ok.
>> +module_i2c_driver(ssd130x_i2c_driver);
>
Best regards,
--
Javier Martinez Canillas
Linux Engineering
Red Hat
