From: Oleksandr Tyshchenko <oleksandr.tyshchenko@globallogic.com>
To: Dirk Behme <dirk.behme@de.bosch.com>
Cc: xen-devel@lists.xenproject.org,
Julien Grall <julien.grall@arm.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Iurii Konovalenko <iurii.konovalenko@globallogic.com>
Subject: Re: [PATCH 1/3] xen/arm: drivers: scif: Remove dead code
Date: Tue, 21 Jun 2016 16:22:01 +0300 [thread overview]
Message-ID: <CAJEb2DFu2-M7GjgNLcMX7sfN8x-TwNhU4eE7+Dnj0q7fyBraLw@mail.gmail.com> (raw)
In-Reply-To: <5c41b7a2-b84d-6e17-43d1-4cc0b4789a6a@de.bosch.com>
On Tue, Jun 21, 2016 at 4:01 PM, Dirk Behme <dirk.behme@de.bosch.com> 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@arm.com>
>> 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@de.bosch.com>
>>>> 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@de.bosch.com>
>>>>> ---
>>>>> 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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next prev parent reply other threads:[~2016-06-21 13:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-21 9:15 [PATCH 1/3] xen/arm: drivers: scif: Remove dead code Dirk Behme
2016-06-21 9:15 ` [PATCH 2/3] xen/arm: drivers: scif: Remove unused variables Dirk Behme
2016-06-21 12:17 ` Julien Grall
2016-06-21 9:15 ` [PATCH 3/3] xen/arm: drivers: scif: Add clock auto detection Dirk Behme
2016-06-21 12:20 ` Julien Grall
2016-06-21 12:30 ` Dirk Behme
2016-06-21 12:33 ` Julien Grall
2016-06-21 10:16 ` [PATCH 1/3] xen/arm: drivers: scif: Remove dead code Oleksandr Tyshchenko
2016-06-21 12:15 ` Julien Grall
2016-06-21 12:54 ` Oleksandr Tyshchenko
2016-06-21 13:01 ` Dirk Behme
2016-06-21 13:22 ` Oleksandr Tyshchenko [this message]
2016-06-21 13:07 ` Julien Grall
2016-06-21 13:11 ` Oleksandr Tyshchenko
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