[PATCH v3] tty: serial: samsung_tty: loopback mode support

[Marek Szyprowski]

On 12.07.2022 02:44, Chanho Park wrote:
>>> +	if (mctrl & TIOCM_LOOP)
>>> +		ucon |= S3C2410_UCON_LOOPBACK;
>>> +	else
>>> +		ucon &= ~S3C2410_UCON_LOOPBACK;
>>> +
>>> +	wr_regl(port, S3C2410_UCON, ucon);
>> S3C2410_UCON must be modified at least under the local_irq_save() or port
>> lock, otherwise it breaks kernel console operation on older Exynos SoCs
>> (especially when DMA mode is used).
>>
>> The above read-modify-write sequence should be replaced with the following
>> pattern:
>>
>>           if (mctrl & TIOCM_LOOP)
>>                   s3c24xx_set_bit(port, S3C2410_UCON_LOOPBACK, S3C2410_UCON);
>>           else
>>                   s3c24xx_clear_bit(port, S3C2410_UCON_LOOPBACK, S3C2410_UCON);
> All the set_mctrl() call can be protected by spin_[un]lock_irq[save/restore] with port->lock.
> So, I think it is not required.

Right. The problem is elsewhere. You used rd_reg(port, S3C2410_UCON) 
instead of rd_regl(port, S3C2410_UCON) what always zeroed upper bits. I 
will send a fix in a few minutes.


Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland