linux-kernel - Re: [PATCH] tty: serial: msm

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Date:   Mon, 20 May 2019 17:20:48 +0200
From:   Jorge Ramirez <jorge.ramirez-ortiz@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Stephen Boyd <sboyd@...nel.org>, agross@...nel.org,
        david.brown@...aro.org, gregkh@...uxfoundation.org,
        jslaby@...e.com, keescook@...omium.org, anton@...msg.org,
        ccross@...roid.com, tony.luck@...el.com,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, khasim.mohammed@...aro.org,
        agsumit@....qualcomm.com
Subject: Re: [PATCH] tty: serial: msm_serial: Fix XON/XOFF

On 5/20/19 17:12, Bjorn Andersson wrote:
> On Mon 20 May 08:11 PDT 2019, Bjorn Andersson wrote:
> 
>> On Mon 20 May 07:58 PDT 2019, Jorge Ramirez wrote:
>>
>>> On 5/20/19 16:56, Jorge Ramirez wrote:
>>>> On 5/20/19 16:51, Stephen Boyd wrote:
>>>>> Quoting Jorge Ramirez-Ortiz (2019-05-20 03:34:35)
>>>>>> When the tty layer requests the uart to throttle, the current code
>>>>>> executing in msm_serial will trigger "Bad mode in Error Handler" and
>>>>>> generate an invalid stack frame in pstore before rebooting (that is if
>>>>>> pstore is indeed configured: otherwise the user shall just notice a
>>>>>> reboot with no further information dumped to the console).
>>>>>>
>>>>>> This patch replaces the PIO byte accessor with the word accessor
>>>>>> already used in PIO mode.
>>>>>
>>>>> Because the hardware only accepts word based accessors and fails
>>>>> otherwise? I can believe that.
>>>>>
>>>>> I wonder if the earlier UART hardware this driver used to support (i.e.
>>>>> pre-DM) would accept byte access to the registers. It's possible, but we
>>>>> don't really care because those boards aren't supported.
>>>>
>>>> ok.
>>>>
>>>> also the PIO path uses iowrite32_rep to write a number of bytes (from 1
>>>> to 4) so I think it is also appropriate to use it for XON/XOFF.
>>>>
>>>>>
>>>>>>
>>>>>> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>
>>>>>> ---
>>>>>
>>>>> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
>>>>>
>>>>>>  drivers/tty/serial/msm_serial.c | 5 ++++-
>>>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
>>>>>> index 109096033bb1..23833ad952ba 100644
>>>>>> --- a/drivers/tty/serial/msm_serial.c
>>>>>> +++ b/drivers/tty/serial/msm_serial.c
>>>>>> @@ -869,10 +870,12 @@ static void msm_handle_tx(struct uart_port *port)
>>>>>>                 else
>>>>>>                         tf = port->membase + UART_TF;
>>>>>>  
>>>>>> +               buf[0] = port->x_char;
>>>>>> +
>>>>>>                 if (msm_port->is_uartdm)
>>>>>>                         msm_reset_dm_count(port, 1);
>>>>>>  
>>>>>> -               iowrite8_rep(tf, &port->x_char, 1);
>>>>>> +               iowrite32_rep(tf, buf, 1);
>>>>>
>>>>> I suppose it's OK to write some extra zeroes here?
>>>>>
>>>>>
>>>>
>>>> yeah, semantically confusing msm_reset_dm_count is what really matters:
>>>> it tells the hardware to only take n bytes (in this case only one) so
>>>> the others will be ignored
>>>
>>> um after I said this, maybe iowrite32_rep should only be applied to
>>> uartdm ... what do you think?
>>>
>>
>> If I read the history correctly this write was a writel() up until
>> 68252424a7c7 ("tty: serial: msm: Support big-endian CPUs").
>>
>> So I think you should just change this back to a iowrite32_rep() and add
>> a Fixes tag.
>>
> 
> I mean...

ok. cool

> 
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> Regards,
> Bjorn
>