linux-kernel - Re: [PATCH v6 6/7] gpio: aspeed: Add the flush write to ensure the write complete.

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Message-ID: <97163102cad92e9bf6cc3609295a27af60c8df7e.camel@codeconstruct.com.au>
Date: Mon, 30 Sep 2024 14:08:18 +0930
From: Andrew Jeffery <andrew@...econstruct.com.au>
To: Billy Tsai <billy_tsai@...eedtech.com>, linus.walleij@...aro.org, 
 brgl@...ev.pl, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
 joel@....id.au, linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org, 
 linux-kernel@...r.kernel.org, BMC-SW@...eedtech.com,
 Peter.Yin@...ntatw.com,  Jay_Zhang@...ynn.com
Subject: Re: [PATCH v6 6/7] gpio: aspeed: Add the flush write to ensure the
 write complete.

On Fri, 2024-09-27 at 19:17 +0800, Billy Tsai wrote:
> Performing a dummy read ensures that the register write operation is fully
> completed, mitigating any potential bus delays that could otherwise impact
> the frequency of bitbang usage. E.g., if the JTAG application uses GPIO to
> control the JTAG pins (TCK, TMS, TDI, TDO, and TRST), and the application
> sets the TCK clock to 1 MHz, the GPIO's high/low transitions will rely on
> a delay function to ensure the clock frequency does not exceed 1 MHz.
> However, this can lead to rapid toggling of the GPIO because the write
> operation is POSTed and does not wait for a bus acknowledgment.
> 
> Signed-off-by: Billy Tsai <billy_tsai@...eedtech.com>

Reviewed-by: Andrew Jeffery <andrew@...econstruct.com.au>