Subject: Re: [PATCH 1/9] mtd: rawnand: brcmnand: Allow SoC to provide I/O operations

From: Miquel Raynal <[email-masked]>
Date: Tue, 4 Jan 2022 09:32:21 +0100

Hi Florian,

[email-masked] wrote on Mon, 3 Jan 2022 09:24:26 -0800:

> On 1/3/2022 8:49 AM, Miquel Raynal wrote:
> > Hi Florian,
> > 
> > [email-masked] wrote on Wed, 22 Dec 2021 16:22:17 -0800:
> >   
> >> Allow a brcmnand_soc instance to provide a custom set of I/O operations
> >> which we will require when using this driver on a BCMA bus which is not
> >> directly memory mapped I/O. Update the nand_{read,write}_reg accordingly
> >> to use the SoC operations if provided.
> >>
> >> Signed-off-by: Florian Fainelli <[email-masked]>
> >> ---
> >>   drivers/mtd/nand/raw/brcmnand/brcmnand.c | 14 ++++++++++++--
> >>   drivers/mtd/nand/raw/brcmnand/brcmnand.h | 23 +++++++++++++++++++++++
> >>   2 files changed, 35 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> >> index f75929783b94..7a1673b1b1af 100644
> >> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> >> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> >> @@ -594,13 +594,18 @@ enum {  
> >>   >>   static inline u32 nand_readreg(struct brcmnand_controller *ctrl, u32 offs)  
> >>   {
> >> +	if (brcmnand_soc_has_ops(ctrl->soc))
> >> +		return brcmnand_soc_read(ctrl->soc, offs);
> >>   	return brcmnand_readl(ctrl->nand_base + offs);
> >>   }  
> >>   >>   static inline void nand_writereg(struct brcmnand_controller *ctrl, u32 offs,  
> >>   				 u32 val)
> >>   {
> >> -	brcmnand_writel(val, ctrl->nand_base + offs);
> >> +	if (brcmnand_soc_has_ops(ctrl->soc))
> >> +		brcmnand_soc_write(ctrl->soc, val, offs);
> >> +	else
> >> +		brcmnand_writel(val, ctrl->nand_base + offs);
> >>   }  
> >>   >>   static int brcmnand_revision_init(struct brcmnand_controller *ctrl)  
> >> @@ -766,13 +771,18 @@ static inline void brcmnand_rmw_reg(struct brcmnand_controller *ctrl,  
> >>   >>   static inline u32 brcmnand_read_fc(struct brcmnand_controller *ctrl, int word)  
> >>   {
> >> +	if (brcmnand_soc_has_ops(ctrl->soc))
> >> +		return brcmnand_soc_read(ctrl->soc, ~0);
> >>   	return __raw_readl(ctrl->nand_fc + word * 4);
> >>   }  
> >>   >>   static inline void brcmnand_write_fc(struct brcmnand_controller *ctrl,  
> >>   				     int word, u32 val)
> >>   {
> >> -	__raw_writel(val, ctrl->nand_fc + word * 4);
> >> +	if (brcmnand_soc_has_ops(ctrl->soc))
> >> +		brcmnand_soc_write(ctrl->soc, val, ~0);
> >> +	else
> >> +		__raw_writel(val, ctrl->nand_fc + word * 4);
> >>   }  
> >>   >>   static inline void edu_writel(struct brcmnand_controller *ctrl,  
> >> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.h b/drivers/mtd/nand/raw/brcmnand/brcmnand.h
> >> index eb498fbe505e..a3f2ad5f6572 100644
> >> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.h
> >> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.h
> >> @@ -11,12 +11,19 @@  
> >>   >>   struct platform_device;  
> >>   struct dev_pm_ops;
> >> +struct brcmnand_io_ops;  
> >>   >>   struct brcmnand_soc {  
> >>   	bool (*ctlrdy_ack)(struct brcmnand_soc *soc);
> >>   	void (*ctlrdy_set_enabled)(struct brcmnand_soc *soc, bool en);
> >>   	void (*prepare_data_bus)(struct brcmnand_soc *soc, bool prepare,
> >>   				 bool is_param);
> >> +	const struct brcmnand_io_ops *ops;
> >> +};
> >> +
> >> +struct brcmnand_io_ops {
> >> +	u32 (*read_reg)(struct brcmnand_soc *soc, u32 offset);
> >> +	void (*write_reg)(struct brcmnand_soc *soc, u32 val, u32 offset);
> >>   };  
> >>   >>   static inline void brcmnand_soc_data_bus_prepare(struct brcmnand_soc *soc,  
> >> @@ -58,6 +65,22 @@ static inline void brcmnand_writel(u32 val, void __iomem *addr)
> >>   		writel_relaxed(val, addr);
> >>   }  
> >>   >> +static inline bool brcmnand_soc_has_ops(struct brcmnand_soc *soc)  
> >> +{
> >> +	return soc && soc->ops && soc->ops->read_reg && soc->ops->write_reg;
> >> +}
> >> +
> >> +static inline u32 brcmnand_soc_read(struct brcmnand_soc *soc, u32 offset)
> >> +{
> >> +	return soc->ops->read_reg(soc, offset);
> >> +}
> >> +
> >> +static inline void brcmnand_soc_write(struct brcmnand_soc *soc, u32 val,
> >> +				      u32 offset)
> >> +{
> >> +	soc->ops->write_reg(soc, val, offset);
> >> +}
> >> +  
> > 
> > It might be worth looking into more optimized ways to do these checks,
> > in particular the read/write_reg ones because you're checking against
> > some static data which cannot be optimized out by the compiler but
> > won't change in the lifetime of the kernel.  
> 
> I suppose I could add an addition if IS_ENABLED(CONFIG_MTD_NAND_BRCMNAND_BCMA) at the front of brcmnand_soc_has_ops(), would that address your concern or you have something else in mind?

I don't like much the #ifdef solution, instead you might think of
static keys, or even better using a regmap. Regmap implementation is
free, you can use either one way or the other and for almost no
overhead compared to the bunch of functions you have here.

Thanks,
Miquèl