Following up

Peilin Ye
2020-10-27T16:51:00Z

Hi Daniel,

More about the 3 things we've discussed before:

1. Cleaning up con_font_op():

(drivers/tty/vt/vt.c)
int con_font_op(struct vc_data *vc, struct console_font_op *op)
{
switch (op->op) {
case KD_FONT_OP_SET:
return con_font_set(vc, op);
case KD_FONT_OP_GET:
return con_font_get(vc, op);
case KD_FONT_OP_SET_DEFAULT:
return con_font_default(vc, op);
case KD_FONT_OP_COPY:
return con_font_copy(vc, op);
}
return -ENOSYS;
}

On Tue, Sep 29, 2020 at 04:38:49PM +0200, Daniel Vetter wrote:
> I think if we change the conf_font_get/set/default/copy functions to not
> take the *op struct (which is take pretty arbitrarily from one of the
> ioctl), but the parameters each needs directly, that would clean up the
> code a _lot_.

This is on my TODO list! One day I came up with some idea about
fbcon.c, so I postponed this a bit...

2. Removing dummy functions, like sisusbdummycon_font_set():

Turns out, before c396a5bf457f ("console: Expand dummy functions for
CFI"), they were just some macros:

-#define SISUSBCONDUMMY (void *)sisusbdummycon_dummy
+static int sisusbdummycon_font_set(struct vc_data *vc,
+ struct console_font *font,
+ unsigned int flags)
+{
+ return 0;
+}

...and they had been there for a very long (10+ years) time. Removing
code like this makes me a bit nervous, and...

On Tue, Sep 29, 2020 at 04:38:49PM +0200, Daniel Vetter wrote:
> This actually does something. tbh I would not be surprises if the
> fb_set utility is the only thing that uses this - with a bit of code
> search we could perhaps confirm this, and delete all the other
> implementations.

...you mentioned code search, where & what should we look at, in order
to confirm it's safe to remove them?

3. Using `font_desc` in `vc_data`:

Our plan for the gradual conversion was to use a helper function to
set font for a vc, but after reviewing the 300-ish occurrence of
`vc_font`, it seems like code doesn't usually set it as a whole:

(drivers/usb/misc/sisusbvga/sisusb_con.c)
[...]
c->vc_font.height = sisusb->current_font_height;
[...]

...that's it! It only cares about the height. There are only 4 or 5
places in fbcon.c that actually set all fields of `vc_font`, like:

vc->vc_font.width = font->width;
vc->vc_font.height = font->height;
vc->vc_font.data = (void *)(p->fontdata = font->data);
vc->vc_font.charcount = 256; /* FIXME Need to support more fonts */

To make it even more complicated, `p` is a `struct fbcon_display *`,
containing yet another font data pointer (`fontdata`) that I think
should be replaced by a `font_desc *`...

In conclusion, I think it's all about a few hard problems in fbcon.c.
I'll keep trying and see how it goes.

Thank you,
Peilin Ye