[U-Boot Patch v2 1/4] fu540: dtsi: spi: add num-cs info to device tree

[Bin Meng]

Hi Sagar,

On Thu, Feb 6, 2020 at 2:17 AM Sagar Kadam <sagar.kadam at sifive.com> wrote:
>
> Hello Bin,
>
> > -----Original Message-----
> > From: Bin Meng <bmeng.cn at gmail.com>
> > Sent: Tuesday, February 4, 2020 5:43 PM
> > To: Sagar Kadam <sagar.kadam at sifive.com>
> > Cc: U-Boot Mailing List <u-boot at lists.denx.de>; Rick Chen
> > <rick at andestech.com>; Paul Walmsley ( Sifive) <paul.walmsley at sifive.com>;
> > Jagan Teki <jagan at amarulasolutions.com>; Anup Patel
> > <anup.patel at wdc.com>
> > Subject: Re: [U-Boot Patch v2 1/4] fu540: dtsi: spi: add num-cs info to device
> > tree
> >
> > Hi Sagar,
> >
> > On Wed, Jan 29, 2020 at 2:02 AM Sagar Shrikant Kadam
> > <sagar.kadam at sifive.com> wrote:
> > >
> > > Add the number of chip select information to spi nodes which can be
> > > used by spi-uclass for error handling if invalid cs number passed from
> > > command.
> > >
> > > Signed-off-by: Sagar Shrikant Kadam <sagar.kadam at sifive.com>
> > > ---
> > >  arch/riscv/dts/fu540-c000.dtsi | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/arch/riscv/dts/fu540-c000.dtsi
> > > b/arch/riscv/dts/fu540-c000.dtsi index afa43c7..9c6ab21 100644
> > > --- a/arch/riscv/dts/fu540-c000.dtsi
> > > +++ b/arch/riscv/dts/fu540-c000.dtsi
> > > @@ -191,6 +191,7 @@
> > >                         clocks = <&prci PRCI_CLK_TLCLK>;
> > >                         #address-cells = <1>;
> > >                         #size-cells = <0>;
> > > +                       num-cs = <1>;
> >
> > Why is this necessary? I can't find the codes that handle the num-cs
> > property.
> The code handling num-cs is a part of patch 2. I intended to keep it separate
> thinking better to isolate dt and c files patches. Please let me know if I need
> to keep it together.
>
> > In the SiFive SPI driver, num_cs is determined from register
> > SIFIVE_SPI_REG_CSDEF.
> >
> The SiFive SPI driver does read the num_cs defined in the register you mentioned.
> but it's hard defined with cs_width, eg: QSPI0 = 1, QSPI1 = 4, QSPI2 = 1.
> I have added the option after sifive_spi_init_hw to read from  device tree as well
> so that if the user want's to change the chip select's (less than that defined in
> SIFIVE_SPI_REG_CSDEF) then it can be done in hifive-unleashed-a00.dtsi
> Please let me know your thoughts over here.
>

My understanding is that "nun-cs" represents the actual number of chip
selects a controller supports. In your patch you changed all 3
controllers num-cs to 1, but they should be 1/4/1 respectively.

I see changes are made in fu540-c000.dtsi. Was such change discussed
in the kernel DT community?

Is this change actually fixing any issue with what we saw on the
Unleashed board?

Regards,
Bin