From: Peter Maydell <1914535@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1914535] Re: PL110 8-bit mode is not emulated correctly
Date: Fri, 19 Feb 2021 17:18:32 -0000 [thread overview]
Message-ID: <161375511284.10946.9838968545913659339.malone@chaenomeles.canonical.com> (raw)
In-Reply-To: 161241593716.24579.2543593740941156934.malonedeb@wampee.canonical.com
Anyway, on first investigation I'm not sure what QEMU's pl11x model is doing wrong. The 8-bit mode is a palette-based setup, where the guest must program in the RGB values it wants to use into the palatte registers as RGB555 data:
https://developer.arm.com/documentation/ddi0293/c/programmer-s-model/register-descriptions/256x16-bit-color-palette-registers?lang=en
and if you add some debug printing to QEMU you can see the guest writing in
a variety of definitely-not-shades-of-grey values to the palette, so it's not surprising that it comes back as not-grey.
I think
https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/amba-clcd.c#L343
is where the driver is writing to the palette and it definitely thinks the display is pseudocolor, not greyscale.
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https://bugs.launchpad.net/bugs/1914535
Title:
PL110 8-bit mode is not emulated correctly
Status in QEMU:
New
Bug description:
When the emulated pl110/pl111 is switched programmatically to 8-bit
color depth mode, the display is drawn green and blue, but the real
PL110 displays grayscale in 8-bit mode.
The bug appears in qemu-system-arm version 3.1.0 (Debian
1:3.1+dfsg-8+deb10u8) and qemu-system-arm version 5.2.50
(v5.2.0-1579-g99ae0cd90d).
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1914535/+subscriptions
next prev parent reply other threads:[~2021-02-19 17:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-04 5:18 [Bug 1914535] [NEW] PL110 8-bit mode is not emulated correctly Vadim Averin
2021-02-15 10:58 ` [Bug 1914535] " Peter Maydell
2021-02-15 17:55 ` Vadim Averin
2021-02-19 16:56 ` Peter Maydell
2021-02-19 17:16 ` Vadim Averin
2021-02-19 17:18 ` Peter Maydell [this message]
2021-02-22 12:08 ` Vadim Averin
2021-02-22 14:04 ` Peter Maydell
2021-02-22 14:04 ` Peter Maydell
2021-02-24 5:45 ` Vadim Averin
2021-02-24 10:53 ` Peter Maydell
2021-03-22 13:43 ` Peter Maydell
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