linux-kernel - Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

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Message-ID: <CAOX-t573QkixRC7xa1KUOYXfL12Q+Ltxph9rX7V8tm2BMoqxgA@mail.gmail.com>
Date:   Fri, 14 Jan 2022 10:22:56 +0800
From:   hammer hsieh <hammerh0314@...il.com>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>, robh+dt@...nel.org,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, p.zabel@...gutronix.de,
        wells.lu@...plus.com, "hammer.hsieh" <hammer.hsieh@...plus.com>
Subject: Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

Jiri Slaby <jirislaby@...nel.org> 於 2022年1月13日 週四 下午7:12寫道：
>
> On 13. 01. 22, 11:56, hammer hsieh wrote:
> >> Could you explain me what posted write is and how does it not matter in
> >> this case?
> >>
> >
> > Each UART ISC register contains
>
> No, you still don't follow what I write. Use your favorite web search
> for "posted write" and/or consult with your HW team.
>

Maybe this time, we are on the same page.
Our SP7021 chipset is designed on ARM Cortex-A7 Quad core.
Register Access through AMBA(AXI bus), and it is non-cached.

Did you mean
case1 have concern about "posted write", and you want to know why it not matter?
case2 will be safer?

Case1 :
spin_lock_irq_save()
writel(0, target register)
spin_unlock_irqrestore()
Case2 :
spin_lock_irq_save()
tmp = readl(target register)
tmp &= ~(bit4 | bit5)
writel(tmp, target register)
spin_unlock_irqrestore()

I test uart port with linux-serial-test tool.
Ex. send char
linux-serial-test -y 0x55 -z 0x31 -p /dev/ttySUPx -b 115200
driver will call from uart startup till uart shutdown.
And it works fine, so I didn't think about "posted write" on Register bus.

> --
> js
> suse labs