Re: [Xen-devel] [PATCH 1/3] xen/arm: drivers: scif: Remove dead code

[Oleksandr Tyshchenko <oleksandr.tyshchenko@xxxxxxxxxxxxxxx>]

On Tue, Jun 21, 2016 at 4:01 PM, Dirk Behme <dirk.behme@xxxxxxxxxxxx> wrote:
> Hello Oleksandr,
>
>
> On 21.06.2016 14:54, Oleksandr Tyshchenko wrote:
>>
>> On Tue, Jun 21, 2016 at 3:15 PM, Julien Grall <julien.grall@xxxxxxx>
>> wrote:
>>>
>>>
>>>
>>> On 21/06/16 11:16, Oleksandr Tyshchenko wrote:
>>>>
>>>>
>>>> Hi, Dirk.
>>>
>>>
>>>
>>> Hello Oleksandr,
>>
>>
>> Hello Julien.
>>>
>>>
>>>
>>>> On Tue, Jun 21, 2016 at 12:15 PM, Dirk Behme <dirk.behme@xxxxxxxxxxxx>
>>>> wrote:
>>>>>
>>>>>
>>>>> In scif_uart_init() uart->baud is set to BAUD_AUTO. So its a basic
>>>>> error
>>>>> if this is different later. Detect this by an ASSERT, but remove the
>>>>> dead code normally never reached.
>>>>>
>>>>> Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
>>>>> ---
>>>>>   xen/drivers/char/scif-uart.c | 23 ++++++-----------------
>>>>>   1 file changed, 6 insertions(+), 17 deletions(-)
>>>>>
>>>>> diff --git a/xen/drivers/char/scif-uart.c
>>>>> b/xen/drivers/char/scif-uart.c
>>>>> index 51a2233..ca88c0f 100644
>>>>> --- a/xen/drivers/char/scif-uart.c
>>>>> +++ b/xen/drivers/char/scif-uart.c
>>>>> @@ -143,23 +143,12 @@ static void __init scif_uart_init_preirq(struct
>>>>> serial_port *port)
>>>>>       scif_writew(uart, SCIF_SCSMR, val);
>>>>>
>>>>>       ASSERT( uart->clock_hz > 0 );
>>>>> -    if ( uart->baud != BAUD_AUTO )
>>>>> -    {
>>>>> -        /* Setup desired Baud rate */
>>>>> -        divisor = uart->clock_hz / (uart->baud << 4);
>>>>> -        ASSERT( divisor >= 1 && divisor <= (uint16_t)UINT_MAX );
>>>>> -        scif_writew(uart, SCIF_DL, (uint16_t)divisor);
>>>>> -        /* Selects the frequency divided clock (SC_CLK external input)
>>>>> */
>>>>> -        scif_writew(uart, SCIF_CKS, 0);
>>>>> -        udelay(1000000 / uart->baud + 1);
>>>>
>>>>
>>>>
>>>> This part of code might be used for people who are not satisfied with
>>>> default baudrate which has been set in U-Boot.
>>>
>>>
>>>
>>> Can you elaborate? If the baud rate is different, it will not be possible
>>> to
>>> get output from U-boot.
>>>
>>>> If we remove this we will take away the opportunity to just change
>>>> uart->baud from BAUD_AUTO to desired one.
>>>
>>>
>>>
>>> I have some doubt that the current code is valid. The clock frequency is
>>> hardcoded (see SCIF_CLK_FREQ), so are you saying that the frequency is
>>> always the same across all the platforms?
>>
>>
>> No.
>>
>> This driver has been initially written for Renesas Lager board based
>> on R-Car H2 SoC which
>> has SCIF compatible UART. And the current code is valid for it. I have
>> tested both auto and
>> variable (38400, 115200) baudrates.
>
>
>
> Could you help me a little to understand this?
>
> The driver has
>
> scif_uart_init()
> {
> ...
> struct scif_uart *uart;
> ...
> uart->baud      = BAUD_AUTO;
> ...
> }
>
> I checked the code for struct scif_uart but it isn't used anywhere outside
> this driver. So uart->baud is a driver local variable, which looks to me
> isn't used anywhere useful.
>
> What have I missed?

Unfortunately, I don't have recent Xen sources right now to be 100%
sure. But, it seems you are right: uart->baud is a driver local
variable.

>
> Best regards
>
> Dirk
>
>
>
>> But, I am afraid that current code won't be suitable for
>> all of the boards which have the same UART IP. It depends at least
>> from clock source
>> (external/internal) and clock frequency.
>>
>>>
>>> I would rather avoid to keep dead code (or not accessible without hacking
>>> Xen). For what is worth, we recently removed a similar code from the
>>> PL011
>>> driver as this should be correctly configured by the firmware.
>>>
>>>>> -    }
>>>>> -    else
>>>>> -    {
>>>>> -        /* Read current Baud rate */
>>>>> -        divisor = scif_readw(uart, SCIF_DL);
>>>>> -        ASSERT( divisor >= 1 && divisor <= (uint16_t)UINT_MAX );
>>>>> -        uart->baud = uart->clock_hz / (divisor << 4);
>>>>> -    }
>>>>> +    ASSERT( uart->baud == BAUD_AUTO );
>>>>> +
>>>>> +    /* Read current Baud rate */
>>>>> +    divisor = scif_readw(uart, SCIF_DL);
>>>>> +    ASSERT( divisor >= 1 && divisor <= (uint16_t)UINT_MAX );
>>>>> +    uart->baud = uart->clock_hz / (divisor << 4);
>>>>>
>>>>>       /* Setup trigger level for TX/RX FIFOs */
>>>>>       scif_writew(uart, SCIF_SCFCR, SCFCR_RTRG11 | SCFCR_TTRG11);
>>>>> --
>>>>> 2.8.0
>>>>>
>>>
>>> Regards,



-- 

Oleksandr Tyshchenko | Embedded Dev
GlobalLogic
www.globallogic.com

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