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Subject: Re: [PATCH v3 6/6] bus: mhi: core: Fix channel device name conflict
To:     Jeffrey Hugo <jhugo@codeaurora.org>,
        manivannan.sadhasivam@linaro.org
Cc:     bbhatt@codeaurora.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1588003153-13139-1-git-send-email-jhugo@codeaurora.org>
 <1588003153-13139-7-git-send-email-jhugo@codeaurora.org>
From:   Hemant Kumar <hemantk@codeaurora.org>
Message-ID: <72519148-a677-bfdf-05fc-f14cc3e3bffd@codeaurora.org>
Date:   Tue, 28 Apr 2020 11:57:53 -0700
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On 4/27/20 8:59 AM, Jeffrey Hugo wrote:
> When multiple instances of the same MHI product are present in a system,
> we can see a splat from mhi_create_devices() - "sysfs: cannot create
> duplicate filename".
> 
> This is because the device names assigned to the MHI channel devices are
> non-unique.  They consist of the channel's name, and the channel's pipe
> id.  For identical products, each instance is going to have the same
> set of channel (both in name and pipe id).
> 
> To fix this, we prepend the device name of the parent device that the
> MHI channels belong to.  Since different instances of the same product
> should have unique device names, this makes the MHI channel devices for
> each product also unique.
> 
> Additionally, remove the pipe id from the MHI channel device name.  This
> is an internal detail to the MHI product that provides little value, and
> imposes too much device specific internal details to userspace.  It is
> expected that channel with a specific name (ie "SAHARA") has a specific
> client, and it does not matter what pipe id that channel is enumerated on.
> The pipe id is an internal detail between the MHI bus, and the hardware.
> The client is not expected to make decisions based on the pipe id, and to
> do so would require the client to have intimate knowledge of the hardware,
> which is inappropiate as it may violate the layering provided by the MHI
> bus.  The limitation of doing this is that each product may only have one
> instance of a channel by a unique name.  This limitation is appropriate
> given the usecases of MHI channels.
> 
> Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
> ---
Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>

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