linux-kernel - Re: [PATCH v2] locking/memory-barriers.txt: Improve documentation for writel() example

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Date:   Thu, 6 Oct 2022 09:00:50 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Parav Pandit <parav@...dia.com>, arnd@...db.de,
        stern@...land.harvard.edu, parri.andrea@...il.com, will@...nel.org,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        paulmck@...nel.org, akiyks@...il.com, dlustig@...dia.com,
        joel@...lfernandes.org, corbet@....net,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v2] locking/memory-barriers.txt: Improve documentation for
 writel() example

On 10/5/22 17:47, Parav Pandit wrote:
> @@ -1927,10 +1927,12 @@ There are some more advanced barrier functions:
>       before we read the data from the descriptor, and the dma_wmb() allows
>       us to guarantee the data is written to the descriptor before the device
>       can see it now has ownership.  The dma_mb() implies both a dma_rmb() and
> -     a dma_wmb().  Note that, when using writel(), a prior wmb() is not needed
> -     to guarantee that the cache coherent memory writes have completed before
> -     writing to the MMIO region.  The cheaper writel_relaxed() does not provide
> -     this guarantee and must not be used here.
> +     a dma_wmb().  Note that, when using writel(), a prior barrier is not
> +     needed to guarantee that the cache coherent memory writes have completed
> +     before writing to the MMIO region.  The cheaper writel_relaxed() does not
> +     provide this guarantee and must not be used here. Hence, writeX() is always
> +     preferred which inserts needed platform specific barrier before writing to
> +     the specified MMIO region.
>  

Did you mean that writeX() is write() function family?

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