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

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Date:   Tue, 26 Feb 2019 15:56:46 +0530
From:   Vignesh R <vigneshr@...com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Rob Herring <robh+dt@...nel.org>
CC:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "tudor.ambarus@...rochip.com" <tudor.ambarus@...rochip.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Nori, Sekhar" <nsekhar@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 3/5] mtd: Add support for Hyperbus memory devices



On 26/02/19 1:03 AM, Sergei Shtylyov wrote:
> On 02/25/2019 09:21 PM, Vignesh R wrote:
> 
> [...]
> 
>>>> 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 R <vigneshr@...com>
> [...]
>>>> diff --git a/drivers/mtd/hyperbus/core.c b/drivers/mtd/hyperbus/core.c
>>>> new file mode 100644
>>>> index 000000000000..d3d44aab7503
>>>> --- /dev/null
>>>> +++ b/drivers/mtd/hyperbus/core.c
> [...]
>>>> +int hb_register_device(struct hb_device *hbdev)
>>>> +{
>>>> +	struct resource res;
>>>> +	struct device *dev;
>>>> +	struct device_node *np;
>>>> +	struct map_info *map;
>>>> +	struct hb_ops *ops;
>>>> +	int err;
>>>> +
>>>> +	if (!hbdev || !hbdev->dev || !hbdev->np) {
>>>> +		pr_err("hyperbus: please fill all the necessary fields!\n");
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>> +	np = hbdev->np;
>>>> +	if (!of_device_is_compatible(np, "cypress,hyperflash"))
>>>> +		return -ENODEV;
>>>> +
>>>> +	hbdev->memtype = HYPERFLASH;
>>>> +
>>>> +	if (of_address_to_resource(np, 0, &res))
>>>
>>>     Isn't the direct mapping property of the HF controller, not of HyperFlash
>>> itself?
>>>
>>
>> As I said in the cover letter, I could not find many examples of HF
>> controllers, but couple of them that I studied provide MMIO access to
>> flash. So, reg property of flash node would represent local address on
>> the HyperBus and controller node would set up ranges properly to provide
>> translation from CS to SoC address space.
>> For example see patch 4/5 where reg property would indicate CS and Size
>> of flash. This scheme is similar to whats described here [1]
>> HBMC controllers usually have different MMIO regions to access flashes
>> connected to different CS. So using ranges for address translation along
>> with flash node describing local address works pretty well.
>>
>> My understanding is that this part of code will be common for most MMIO
>> based HB controllers and hence made part of core layer. But, if
>> controllers uses different IO space for read vs write, then this needs a
>> bit of thinking. In that case, mapping needs to be moved to controller
>> drivers.
>>
>> [1]https://elinux.org/Device_Tree_Usage#Ranges_.28Address_Translation.29
>>
>>>> +		return -EINVAL;
>>>> +
>>>> +	dev = hbdev->dev;
>>>> +	map = &hbdev->map;
>>>> +	map->size = resource_size(&res);
>>>> +	map->virt = devm_ioremap_resource(dev, &res);
>>>> +	if (IS_ERR(map->virt))
>>>> +		return PTR_ERR(map->virt);
>>>> +
>>>> +	map->name = dev_name(dev);
>>>> +	map->bankwidth = 2;
>>>> +
>>>> +	simple_map_init(map);
>>>
>>>    It's not that simple, I'm afraid -- e.g. Renesas RPC-IF has read and write
>>> mappings in the separate memory resources.
>>>
>>
>> Hmm, could you point me to public datasheet of the controller?
> 
>    See chapter 20 in [1]. Note that it's not the same SoC I'm developing for (R-Car
> gen3 family, with NDA docs) but should be mostly the same RPC-IF core.
> 
> [1] https://www.renesas.com/us/en/doc/products/mpumcu/doc/rz/r01uh0746ej0200-rza2m.pdf?key=74862185b5e22ad09e648d21a35de615

Thanks for the info!

> 
>> simple_map_init() provides default implementation for map operations
>> which is overridden, if hb_ops is populated.
>> I think, Renesas RPC-IF can populate custom hb_ops struct and use
>> appropriate MMIO base for read vs write, while still reusing the map
>> framework. Wouldnt that work?
> 
>    It probably would...
> 


Looking at above link, I see there are two HBMC controllers on Renesas
SoC. One is a dedicated HBMC controller(chapter 21) very similar to that
on TI SoC and a SPI Multi I/O Bus Controller (chapter 20) that also
supports Hyperbus protocol.

AFAICS, passing custom hb_ops is good enough to support both HW needs.
Let me know if something is missing. I would greatly appreciate if you
could test this series with your HW.



-- 
Regards
Vignesh