linux-kernel - Re: [PATCH v2 1/2] spi: Add Renesas R-Car Gen3 RPC SPI controller driver

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Date:   Wed, 5 Dec 2018 14:15:37 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     masonccyang@...c.com.tw,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Mark Brown <broonie@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Simon Horman <horms@...ge.net.au>, juliensu@...c.com.tw,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>, zhengxunli@...c.com.tw
Subject: Re: [PATCH v2 1/2] spi: Add Renesas R-Car Gen3 RPC SPI controller driver

Hi Marek,

On Wed, Dec 5, 2018 at 1:57 PM Marek Vasut <marek.vasut@...il.com> wrote:
> On 12/05/2018 08:44 AM, masonccyang@...c.com.tw wrote:
> >> "Marek Vasut" <marek.vasut@...il.com>
> >> 2018/12/05 上午 10:04
> >> On 12/03/2018 10:18 AM, Mason Yang wrote:
> >> > Add a driver for Renesas R-Car Gen3 RPC SPI controller.
> >> >
> >> > Signed-off-by: Mason Yang <masonccyang@...c.com.tw>

> >> > +static void rpc_spi_hw_init(struct rpc_spi *rpc)
> >> > +{
> >> > +   /*
> >> > +    * NOTE: The 0x260 are undocumented bits, but they must be set.
> >> > +    *   RPC_PHYCNT_STRTIM is strobe timing adjustment bit,
> >> > +    *   0x0 : the delay is biggest,
> >> > +    *   0x1 : the delay is 2nd biggest,
> >> > +    *   0x3 or 0x6 is a recommended value.
> >> > +    */
> >>
> >> Doesn't this vary by SoC ? I think H3 ES1.0 had different value here,
> >> but I might be wrong.
> >
> > I check the Renesas bare-metal code, mini_monitor v4.01.
> > It set 0x03 or 0x0 and I test them w/ 0x0, 0x3 and 0x6 are all OK.
>
> Shouldn't this somehow use the soc_device_match() then and configure it
> accordingly for various chips ? Like eg. the r8a7795-cpg-mssr driver does.

Please don't use soc_device_match() for per-SoC configuration, if
you already have of_device_id.data.

BTW, this drivers support r8a7795 only (for now), as per the compatible
value.

> >> > +#ifdef CONFIG_RESET_CONTROLLER
> >>
> >> Just make the driver depend on reset controller.
> >
> > ?
> > please refer to
> > https://github.com/torvalds/linux/blob/master/drivers/clk/renesas/renesas-cpg-mssr.c
> >
> > line 124 ~ 126
>
> This seems like a stopgap measure for systems which do not have a reset
> api compatible controller. Geert ?

So far CONFIG_RESET_CONTROLLER is optional.


> >> > +static int rpc_spi_io_xfer(struct rpc_spi *rpc,
> >> > +            const void *tx_buf, void *rx_buf)
> >> > +{
> >> > +   u32 smenr, smcr, data, pos = 0;
> >> > +   int ret = 0;
> >> > +
> >> > +   regmap_write(rpc->regmap, RPC_CMNCR, RPC_CMNCR_MD | RPC_CMNCR_SFDE |
> >> > +              RPC_CMNCR_MOIIO_HIZ | RPC_CMNCR_IOFV_HIZ |
> >> > +              RPC_CMNCR_BSZ(0));
> >> > +   regmap_write(rpc->regmap, RPC_SMDRENR, 0x0);
> >> > +   regmap_write(rpc->regmap, RPC_SMCMR, rpc->cmd);
> >> > +   regmap_write(rpc->regmap, RPC_SMDMCR, rpc->dummy);
> >> > +   regmap_write(rpc->regmap, RPC_SMADR, rpc->addr);
> >> > +
> >> > +   if (tx_buf) {
> >> > +      smenr = rpc->smenr;
> >> > +
> >> > +      while (pos < rpc->xferlen) {
> >> > +         u32 nbytes = rpc->xferlen  - pos;
> >> > +
> >> > +         regmap_write(rpc->regmap, RPC_SMWDR0,
> >> > +                 *(u32 *)(tx_buf + pos));
> >>
> >> *(u32 *) cast is probably not needed , fix casts globally.
> >
> > It must have it!
>
> Why ?

Else you get a compiler warning, as tx_bug is void *.

> >> > +#ifdef CONFIG_PM_SLEEP
> >> > +static int rpc_spi_suspend(struct device *dev)
> >> > +{
> >> > +   struct platform_device *pdev = to_platform_device(dev);
> >> > +   struct spi_master *master = platform_get_drvdata(pdev);
> >> > +
> >> > +   return spi_master_suspend(master);
> >>
> >> Won't the SPI NOR lose state across suspend ? Is that a problem ?
> >
> > I don't think so.
> > Because when the device is not in operation and CS# is high,
> > it is put in stand-by mode.
>
> Is the power to the SPI NOR retained ?

Not if PSCI system suspend turns of power to the SoC.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds