linux-kernel - Re: [PATCH v2 3/3] efi: earlycon: Add support for generic framebuffers and move to console subsystem

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Date:   Sat, 6 Aug 2022 23:37:35 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Markuss Broks <markuss.broks@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Helge Deller <deller@....de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Michal Suchanek <msuchanek@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Wei Ming Chen <jj251510319013@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Tony Lindgren <tony@...mide.com>,
        Linux Documentation List <linux-doc@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        "open list:FRAMEBUFFER LAYER" <linux-fbdev@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v2 3/3] efi: earlycon: Add support for generic
 framebuffers and move to console subsystem

On Sat, Aug 6, 2022 at 6:38 PM Markuss Broks <markuss.broks@...il.com> wrote:
>
> Add early console support for generic linear framebuffer devices.
> This driver supports probing from cmdline early parameters
> or from the device-tree using information in simple-framebuffer node.
> The EFI functionality should be retained in whole.
> The driver was disabled on ARM because of a bug in early_ioremap

We refer to functions like func().

> implementation on ARM and on IA64 because of lack of early_memremap_prot.

Ditto.

...

> +#include <asm/early_ioremap.h>

Can it be placed after linux/* ones?

> +#include <linux/console.h>
> +#include <linux/efi.h>
> +#include <linux/font.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
> +#include <linux/serial_core.h>
> +#include <linux/screen_info.h>

...

> +static int __init simplefb_earlycon_remap_fb(void)
> +{
> +       unsigned long mapping;

+ Blank line.

> +       /* bail if there is no bootconsole or it has been disabled already */
> +       if (!earlycon_console || !(earlycon_console->flags & CON_ENABLED))
> +               return 0;
> +
> +       if (region_intersects(info.phys_base, info.size,
> +                             IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE) == REGION_INTERSECTS)
> +               mapping = MEMREMAP_WB;
> +       else
> +               mapping = MEMREMAP_WC;

> +       info.virt_base = memremap(info.phys_base, info.size, mapping);
> +
> +       return info.virt_base ? 0 : -ENOMEM;

Easier to read the standard pattern:

  if (!info.virt_base)
    return -ENOMEM;

  return 0;

> +}

...

> +static void simplefb_earlycon_write_char(u8 *dst, unsigned char c, unsigned int h)
> +{
> +       const u8 *src;
> +       int m, n, bytes;
> +       u8 x;
> +
> +       bytes = BITS_TO_BYTES(font->width);
> +       src = font->data + c * font->height * bytes + h * bytes;
> +
> +       for (m = 0; m < font->width; m++) {
> +               n = m % 8;
> +               x = *(src + m / 8);

I would write it as

  x = src[m / 8];

> +               if ((x >> (7 - n)) & 1)

> +                       memset(dst, 0xff, (info.depth / 8));

Too many parentheses.

> +               else
> +                       memset(dst, 0, (info.depth / 8));

Ditto.

> +               dst += (info.depth / 8);

Ditto.

> +       }
> +}

-- 
With Best Regards,
Andy Shevchenko