linux-kernel - Re: [PATCH v3 6/6] bus: mhi: core: Fix channel device name conflict

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Date:   Thu, 30 Apr 2020 22:31:30 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     hemantk@...eaurora.org, bbhatt@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/6] bus: mhi: core: Fix channel device name conflict

On Mon, Apr 27, 2020 at 09:59:13AM -0600, 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@...eaurora.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Thanks,
Mani

> ---
>  drivers/bus/mhi/core/main.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 580d72b..0ac0643 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -327,7 +327,8 @@ void mhi_create_devices(struct mhi_controller *mhi_cntrl)
>  
>  		/* Channel name is same for both UL and DL */
>  		mhi_dev->chan_name = mhi_chan->name;
> -		dev_set_name(&mhi_dev->dev, "%04x_%s", mhi_chan->chan,
> +		dev_set_name(&mhi_dev->dev, "%s_%s",
> +			     dev_name(mhi_cntrl->cntrl_dev),
>  			     mhi_dev->chan_name);
>  
>  		/* Init wakeup source if available */
> -- 
> Qualcomm Technologies, Inc. is a member of the
> Code Aurora Forum, a Linux Foundation Collaborative Project.