linux-kernel - Re: [PATCH v8 3/5] mtd: Add support for HyperBus memory devices

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Message-ID: <e5a7866d-bc34-887d-31d3-de4f745c8d65@cogentembedded.com>
Date:   Thu, 11 Jul 2019 22:26:27 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Rob Herring <robh+dt@...nel.org>
Cc:     linux-mtd@...ts.infradead.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        devicetree@...r.kernel.org, Mason Yang <masonccyang@...c.com.tw>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Tokunori Ikegami <ikegami.t@...il.com>
Subject: Re: [PATCH v8 3/5] mtd: Add support for HyperBus memory devices

Hello!

On 06/25/2019 10:57 AM, Vignesh Raghavendra wrote:

> Cypress' HyperBus is Low Signal Count, High Performance Double Data Rate
> Bus interface between a host system master and one or more slave
> interfaces. HyperBus is used to connect microprocessor, microcontroller,
> or ASIC devices with random access NOR flash memory (called HyperFlash)
> or self refresh DRAM (called HyperRAM).
> 
> Its a 8-bit data bus (DQ[7:0]) with  Read-Write Data Strobe (RWDS)
> signal and either Single-ended clock(3.0V parts) or Differential clock
> (1.8V parts). It uses ChipSelect lines to select b/w multiple slaves.
> At bus level, it follows a separate protocol described in HyperBus
> specification[1].
> 
> HyperFlash follows CFI AMD/Fujitsu Extended Command Set (0x0002) similar
> to that of existing parallel NORs. Since HyperBus is x8 DDR bus,
> its equivalent to x16 parallel NOR flash with respect to bits per clock
> cycle. But HyperBus operates at >166MHz frequencies.
> HyperRAM provides direct random read/write access to flash memory
> array.
> 
> But, HyperBus memory controllers seem to abstract implementation details
> and expose a simple MMIO interface to access connected flash.
> 
> Add support for registering HyperFlash devices with MTD framework. MTD
> maps framework along with CFI chip support framework are used to support
> communicating with flash.
> 
> Framework is modelled along the lines of spi-nor framework. HyperBus
> memory controller (HBMC) drivers calls hyperbus_register_device() to
> register a single HyperFlash device. HyperFlash core parses MMIO access
> information from DT, sets up the map_info struct, probes CFI flash and
> registers it with MTD framework.
> 
> Some HBMC masters need calibration/training sequence[3] to be carried
> out, in order for DLL inside the controller to lock, by reading a known
> string/pattern. This is done by repeatedly reading CFI Query
> Identification String. Calibration needs to be done before trying to detect
> flash as part of CFI flash probe.
> 
> HyperRAM is not supported at the moment.
> 
> HyperBus specification can be found at[1]
> HyperFlash datasheet can be found at[2]
> 
> [1] https://www.cypress.com/file/213356/download
> [2] https://www.cypress.com/file/213346/download
> [3] http://www.ti.com/lit/ug/spruid7b/spruid7b.pdf
>     Table 12-5741. HyperFlash Access Sequence
> 
> Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
[...]

> diff --git a/drivers/mtd/hyperbus/hyperbus-core.c b/drivers/mtd/hyperbus/hyperbus-core.c
> new file mode 100644
> index 000000000000..63a9e64895bc
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/hyperbus-core.c
> @@ -0,0 +1,154 @@
[...]
> +int hyperbus_register_device(struct hyperbus_device *hbdev)
> +{
[...]
> +	map->name = dev_name(dev);
> +	map->bankwidth = 2;

   I think this should really be 1, judging on the comment to that field (and on
Cogent's own RPC-IF HF driver).

> +	map->device_node = np;

[...]

MBR, Sergei