[PATCH 1/1][SRU][M] UBUNTU: SAUCE: platform/x86: dell-uart-backlight: add small delay after write command

[Andrea Righi]

On Thu, Sep 14, 2023 at 06:13:41PM +0800, AceLan Kao wrote:
> From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bug/2035299
> 
> After applying fbf84fb368923 ("UBUNTU: SAUCE: platform/x86:
> dell-uart-backlight: replace chars_in_buffer() with flush_chars()"), it
> seems that the read() command may fail to receive a response, even when
> increasing the retry times. It never gets a response when it fails.
> 
> To fix this, try adding a small delay after the write() function as a workaround.

I'm wondering if there's a better way to determine when the "write"
actually completed, so that we can safely issue a read without doing the
msleep() that is often a bit unpredictable.

If msleep() is really the only way to do it, why don't we put that at
the end of dell_uart_write()? I suppose any write would be affected by
this issue potentially...

Thanks,
-Andrea

> 
> Fixes: fbf84fb368923 ("UBUNTU: SAUCE: platform/x86: dell-uart-backlight: replace chars_in_buffer() with flush_chars()")
> Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao at canonical.com>
> ---
>  drivers/platform/x86/dell/dell-uart-backlight.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
> index 120701e5b8b13..c489f7997767f 100644
> --- a/drivers/platform/x86/dell/dell-uart-backlight.c
> +++ b/drivers/platform/x86/dell/dell-uart-backlight.c
> @@ -248,6 +248,7 @@ static int dell_uart_set_bl_power(struct backlight_device *bd, int power)
>  	}
>  
>  	dell_uart_write(uart, bl_cmd->cmd, bl_cmd->tx_len);
> +	msleep(1);
>  	rx_len = dell_uart_read(uart, bl_cmd->ret, bl_cmd->rx_len);
>  
>  	mutex_unlock(&dell_pdata->brightness_mutex);
> @@ -275,6 +276,7 @@ static int dell_uart_get_brightness(struct backlight_device *bd)
>  	}
>  
>  	dell_uart_write(uart, bl_cmd->cmd, bl_cmd->tx_len);
> +	msleep(1);
>  	rx_len = dell_uart_read(uart, bl_cmd->ret, bl_cmd->rx_len);
>  
>  	mutex_unlock(&dell_pdata->brightness_mutex);
> @@ -304,6 +306,7 @@ static int dell_uart_update_status(struct backlight_device *bd)
>  	}
>  
>  	dell_uart_write(uart, bl_cmd->cmd, bl_cmd->tx_len);
> +	msleep(1);
>  	rx_len = dell_uart_read(uart, bl_cmd->ret, bl_cmd->rx_len);
>  
>  	mutex_unlock(&dell_pdata->brightness_mutex);
> @@ -330,6 +333,7 @@ static int dell_uart_show_firmware_ver(struct dell_uart_backlight *dell_pdata)
>  	}
>  
>  	dell_uart_write(uart, bl_cmd->cmd, bl_cmd->tx_len);
> +	msleep(1);
>  	while (retry-- > 0) {
>  		/* first byte is data length */
>  		dell_uart_read(uart, bl_cmd->ret, 1);
> @@ -371,6 +375,7 @@ static int dell_uart_get_display_mode(struct dell_uart_backlight *dell_pdata)
>  		}
>  
>  		dell_uart_write(uart, bl_cmd->cmd, bl_cmd->tx_len);
> +		msleep(1);
>  		rx_len = dell_uart_read(uart, bl_cmd->ret, bl_cmd->rx_len);
>  
>  		mutex_unlock(&dell_pdata->brightness_mutex);
> -- 
> 2.34.1
> 
> 
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