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 09:57:55 +0100

Hi Miquel,

[email-masked] wrote on 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.

Maybe regmaps will actually be slower than these regular if's. Perhaps
static keys are the best option?

Cheers,
Miquèl