linux-kernel - Re: [RFC 4/8] doc: fpga-mgr: separate getting/locking FPGA manager

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Date:   Fri, 17 Feb 2017 11:14:02 -0600
From:   "Li, Yi" <yi1.li@...ux.intel.com>
To:     Alan Tull <atull@...nel.org>,
        Moritz Fischer <moritz.fischer@...us.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     linux-kernel@...r.kernel.org, linux-fpga@...r.kernel.org
Subject: Re: [RFC 4/8] doc: fpga-mgr: separate getting/locking FPGA manager

hi Alan


On 2/15/2017 10:14 AM, Alan Tull wrote:
> Document that getting a reference to a FPGA Manager has been
> separated from locking the FPGA Mangager for use.
>
> fpga_mgr_lock/unlock functions get/release mutex.
>
> of_fpga_mgr_get, fpga_mgr_get, and fpga_mgr_put no longer lock
> the FPGA manager mutex.
>
> This makes it more straigtforward to save a reference to
> a FPGA manager and only attempting to lock it when programming
> the FPGA.

New to the FPGA world, but I like the idea of shorter lock. Separating 
the lock from fpga_mgr_get will give underline FPGA device drivers more 
flexibility to acquire the mgr pointer.
One newbie question, since the underline FPGA device driver does the 
fpga_mgr_register during probe, each manager instance belongs to that 
FPGA device only. What's the use to keep tracking the usage reference 
with fpga_mgr_put/get function, or is it enough to increase/decrease dev 
reference count in fpga_mgr_register/unregister function?

Thanks,
Yi

>
> Signed-off-by: Alan Tull <atull@...nel.org>
> ---
>   Documentation/fpga/fpga-mgr.txt | 19 ++++++++++++++++++-
>   1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/fpga/fpga-mgr.txt b/Documentation/fpga/fpga-mgr.txt
> index 78f197f..06d5d5b 100644
> --- a/Documentation/fpga/fpga-mgr.txt
> +++ b/Documentation/fpga/fpga-mgr.txt
> @@ -53,13 +53,26 @@ To get/put a reference to a FPGA manager:
>   	struct fpga_manager *of_fpga_mgr_get(struct device_node *node);
>   	struct fpga_manager *fpga_mgr_get(struct device *dev);
>   
> -Given a DT node or device, get an exclusive reference to a FPGA manager.
> +Given a DT node or device, get an reference to a FPGA manager.  Pointer
> +can be saved until you are ready to program the FPGA.
>   
>   	void fpga_mgr_put(struct fpga_manager *mgr);
>   
>   Release the reference.
>   
>   
> +To get exclusive control of a FPGA manager:
> +-------------------------------------------
> +
> +	int fpga_mgr_lock(struct fpga_magager *mgr);
> +
> +Call fpga_mgr_lock and verify that it returns 0 before attempting to
> +program the FPGA.
> +
> +	void fpga_mgr_unlock(struct fpga_magager *mgr);
> +
> +Call fpga_mgr_unlock when done programming the FPGA.
> +
>   To register or unregister the low level FPGA-specific driver:
>   -------------------------------------------------------------
>   
> @@ -95,11 +108,13 @@ int ret;
>   
>   /* Get exclusive control of FPGA manager */
>   struct fpga_manager *mgr = of_fpga_mgr_get(mgr_node);
> +ret = fpga_mgr_lock(mgr);
>   
>   /* Load the buffer to the FPGA */
>   ret = fpga_mgr_buf_load(mgr, &info, buf, count);
>   
>   /* Release the FPGA manager */
> +fpga_mgr_unlock(mgr);
>   fpga_mgr_put(mgr);
>   
>   
> @@ -124,11 +139,13 @@ int ret;
>   
>   /* Get exclusive control of FPGA manager */
>   struct fpga_manager *mgr = of_fpga_mgr_get(mgr_node);
> +ret = fpga_mgr_lock(mgr);
>   
>   /* Get the firmware image (path) and load it to the FPGA */
>   ret = fpga_mgr_firmware_load(mgr, &info, path);
>   
>   /* Release the FPGA manager */
> +fpga_mgr_unlock(mgr);
>   fpga_mgr_put(mgr);
>   
>