From: Julien Grall <julien.grall@arm.com>
To: Dirk Behme <dirk.behme@de.bosch.com>,
xen-devel@lists.xenproject.org,
Stefano Stabellini <sstabellini@kernel.org>
Cc: Oleksandr Tyshchenko <oleksandr.tyshchenko@globallogic.com>,
Iurii Konovalenko <iurii.konovalenko@globallogic.com>
Subject: Re: [PATCH 3/3] xen/arm: drivers: scif: Add clock auto detection
Date: Tue, 21 Jun 2016 13:33:07 +0100 [thread overview]
Message-ID: <57693403.9060109@arm.com> (raw)
In-Reply-To: <cd34add7-5999-595e-663d-c00985d9219f@de.bosch.com>
On 21/06/16 13:30, Dirk Behme wrote:
>>> diff --git a/xen/drivers/char/scif-uart.c b/xen/drivers/char/scif-uart.c
>>> index bc157fe..678f46b 100644
>>> --- a/xen/drivers/char/scif-uart.c
>>> +++ b/xen/drivers/char/scif-uart.c
>>> @@ -107,8 +107,19 @@ static void __init scif_uart_init_preirq(struct
>>> serial_port *port)
>>> scif_readw(uart, SCIF_SCLSR);
>>> scif_writew(uart, SCIF_SCLSR, 0);
>>>
>>> - /* Select Baud rate generator output as a clock source */
>>> - scif_writew(uart, SCIF_SCSCR, SCSCR_CKE10);
>>> + /*
>>> + * Select Baud rate generator output as a clock source
>>> + * The clock source can be an internal or external clock.
>>> + * Depending on this the DL register is either 0 or contains
>>> + * the divisor. I.e. we can use this to detect the clock
>>> + * source and based on this can configure the CKE[1:0] bits
>>> + * of the SCSCR register.
>>> + */
>>> + if ( scif_readw(uart, SCIF_DL) )
>>> + scif_writew(uart, SCIF_SCSCR, SCSCR_CKE10); /* External clk */
>>> + else
>>> + scif_writew(uart, SCIF_SCSCR, SCSCR_CKE00); /* Internal clk */
>>
>> Why would we need to select the baud rate generator if the baud has been
>> configured by the firmware?
>
>
> Just to get the correct understanding: The proposal is to just remove
> the code which (wrongly) overwrites the correct settings done by the
> firmware?
>
> I.e. instead of doing the same thing the firmware is already doing,
> again (the if .. else ), the proposal is simply dropping the
>
>
> - /* Select Baud rate generator output as a clock source */
> - scif_writew(uart, SCIF_SCSCR, SCSCR_CKE10);
>
> ?
Yes. However I don't have any spec in hand so I am not sure if it is
correct.
Regards,
--
Julien Grall
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next prev parent reply other threads:[~2016-06-21 12:33 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 [this message]
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
2016-06-21 13:07 ` Julien Grall
2016-06-21 13:11 ` Oleksandr Tyshchenko
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