netdev - Re: [PATCH net-next 2/4] io: add function to flush the write combine buffer to device immediately

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Message-ID: <20210730094222.GB8570@arm.com>
Date:   Fri, 30 Jul 2021 10:42:22 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Guangbin Huang <huangguangbin2@...wei.com>
Cc:     davem@...emloft.net, kuba@...nel.org, will@...nel.org,
        maz@...nel.org, mark.rutland@....com, dbrazdil@...gle.com,
        qperret@...gle.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        lipeng321@...wei.com
Subject: Re: [PATCH net-next 2/4] io: add function to flush the write combine
 buffer to device immediately

On Fri, Jul 30, 2021 at 11:14:22AM +0800, Guangbin Huang wrote:
> From: Xiongfeng Wang <wangxiongfeng2@...wei.com>
> 
> Device registers can be mapped as write-combine type. In this case, data
> are not written into the device immediately. They are temporarily stored
> in the write combine buffer and written into the device when the buffer
> is full. But in some situation, we need to flush the write combine
> buffer to device immediately for better performance. So we add a general
> function called 'flush_wc_write()'. We use DGH instruction to implement
> this function for ARM64.

Isn't this slightly misleading? IIUC DGH does not guarantee flushing, it
just prevents writes merging (maybe this was already discussed on the
previous RFC).

-- 
Catalin