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

[Marek Vasut]

On 10/28/24 1:25 AM, Weijie Gao wrote:
> Hi Daniel,
> 
> On Sat, 2024-10-26 at 20:23 +0100, Daniel Golle wrote:
>> External email : Please do not click links or open attachments until
>> you have verified the sender or the content.
>>
>>
>> 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.
Does CONFIG_SERIAL_RX_BUFFER help with those overflows ?