[PATCH] menu: fix the logic checking whether ESC key is pressed

[Weijie Gao]

Hi Daniel,

On Sat, 2024-10-26 at 20:23 +0100, Daniel Golle wrote:
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> 
> Hi!
> 
> On Mon, Oct 21, 2024 at 08:56:42AM +0800, Weijie Gao wrote:
> > It's observed that the bootmenu on a serial console sometimes
> > incorrectly quitted with superfluous characters filled to command
> > line input:
> > 
> > >  *** U-Boot Boot Menu ***
> > > 
> > >      1. Startup system (Default)
> > >      2. Upgrade firmware
> > >      3. Upgrade ATF BL2
> > >      4. Upgrade ATF FIP
> > >      5. Load image
> > >      0. U-Boot console
> > > 
> > > 
> > >  Press UP/DOWN to move, ENTER to select, ESC to quit
> > > MT7988> [B
> > 
> > Analysis shows it was caused by the wrong logic of bootmenu_loop:
> > 
> > At first the bootmenu_loop received the first ESC char correctly.
> > 
> > However, during the second call to bootmenu_loop, there's no data
> > in the UART Rx FIFO. Due to the low baudrate, the second char of
> > the down array key sequence hasn't be fully received.
> > 
> > But bootmenu_loop just did a mdelay(10), and then treated it as a
> > single ESC key press event. It didn't even try tstc() again after
> > the 10ms timeout.
> > 
> > This patch fixes this issue by letting bootmenu_loop check tstc()
> > twice.
> 
> The patch helps to fix the problem when dealing with single key
> presses. However, apparently this is not enough to fix the issue in
> all situations. I still manage to drop into U-Boot console with an
> extra '[A' when simply holding down the arrow-up key for a while.
> 

Holding down the arrow-up key for a while can cause the PC to send
large amounts of data to the UART Rx FIFO. Since filogic UARTs usually
have only 32 bytes FIFO, it's very easy to cause Rx FIFO overflow,
and then you'll still be dropped into U-Boot console due to data loss. 
I've already confirmed this during solving this issue and this can only
be solved by increasing the baudrate.