From: Julien Grall <julien.grall@arm.com>
To: Amit Tomer <amittomer25@gmail.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
wei.liu2@citrix.com, konrad.wilk@oracle.com,
George Dunlap <George.Dunlap@eu.citrix.com>,
ian.jackson@eu.citrix.com, tim@xen.org,
Andrew Cooper <andrew.cooper3@citrix.com>,
Jan Beulich <jbeulich@suse.com>,
Andre Przywara <andre.przywara@arm.com>,
xen-devel@lists.xenproject.org
Subject: Re: [RFC PATCH 2/2] xen/arm: Add MESON UART driver for Amlogic S905 SoC
Date: Tue, 9 Oct 2018 11:25:57 +0100 [thread overview]
Message-ID: <8f61a00d-b5e7-6b83-e6e4-1bf2473f4576@arm.com> (raw)
In-Reply-To: <CABHD4K-zACRqA2mRNnALY3s5ZrReMYe2g67WLf9rA_U8q=wfNA@mail.gmail.com>
Hi,
On 04/10/2018 08:11, Amit Tomer wrote:
>>>>> + reg = meson_s905_read(uart, UART_CONTROL);
>>>>> + reg &= ~(UART_RX_RST | UART_TX_RST | UART_CLEAR_ERR);
>>>>
>>>>
>>>> I am not sure why you are clearing those bits. AFAIU, init_preirq will reset
>>>> the serials, so you want to set thoses bits. This seems to be confirmed by
>>>> Linux in meson_uart_reset.
>>>
>>> Idea here is to set these bits to their default values(which is 0 ) and if you
>>> look at other drivers in XEN, it seems to be done same thing(clear
>>> those bits) with them.
>>
>> Are you sure about this? RX_RST and TX_RST are bit to reset the
>> transmission and receive path. Looking at a couple of different drivers
>> (cache-uart.c and mvebu-uart.c), those 2 bits are set and I suspect be
>> cleared by the hardware once reset.
>
> It's bit confusing to me, eventually Linux driver seems to clear those bits
But it sets them right before hand. What does the spec says about those
bits?
Overall, I feels to me it is better to mimic the Linux driver as I am
quite confident that the driver is doing the right thing.
Cheers,
--
Julien Grall
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next prev parent reply other threads:[~2018-10-09 10:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-07 17:07 [RFC PATCH 0/2] xen/arm64: Add Support for Amlogic S905 SoC Amit Singh Tomar
2018-08-07 17:07 ` [RFC PATCH 1/2] xen/arm: Add Amlogic S905 SoC early printk support Amit Singh Tomar
2018-08-14 10:01 ` Julien Grall
2018-08-20 9:16 ` Amit Tomer
2018-08-22 9:52 ` Julien Grall
2018-09-12 6:43 ` Amit Tomer
2018-09-12 9:12 ` Julien Grall
2018-10-22 23:31 ` André Przywara
2018-11-17 8:47 ` Amit Tomer
2018-08-07 17:07 ` [RFC PATCH 2/2] xen/arm: Add MESON UART driver for Amlogic S905 SoC Amit Singh Tomar
2018-08-08 10:05 ` Jan Beulich
2018-08-14 10:17 ` Julien Grall
2018-08-20 8:12 ` Amit Tomer
2018-08-22 10:00 ` Julien Grall
2018-10-04 7:11 ` Amit Tomer
2018-10-09 10:25 ` Julien Grall [this message]
2018-10-22 23:31 ` André Przywara
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