Re: [PATCH 2/8] mtd: cfi_flash: allow 0x0 mapping

[Lucas Stach <dev@lynxeye.de>]

Am Montag, den 09.11.2020, 14:44 +0100 schrieb Rouven Czerwinski:
> Annotate the different read and write functions with
> zero_page_{access/faulting}. This allows the cfi_flash driver to be used
> on the QEMU virt machine with an enabled MMU.

I don't like this zero-page access allow in a driver at all. If you
have some free address space somewhere, you could also solve this issue
by remapping the IO resource to somewhere else in the address space,
deviating from the 1:1 mapping. The Tegra PCIe host driver does this,
if you need some inspiration.

Regards,
Lucas

> Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
> ---
>  drivers/mtd/nor/cfi_flash.c |  6 ++++++
>  drivers/mtd/nor/cfi_flash.h | 18 ++++++++++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/mtd/nor/cfi_flash.c b/drivers/mtd/nor/cfi_flash.c
> index 225b03ec3d..2fcbd13e46 100644
> --- a/drivers/mtd/nor/cfi_flash.c
> +++ b/drivers/mtd/nor/cfi_flash.c
> @@ -896,8 +896,10 @@ static int cfi_mtd_read(struct mtd_info *mtd, loff_t from, size_t len,
>  {
>  	struct flash_info *info = container_of(mtd, struct flash_info, mtd);
>  
> +	zero_page_access();
>  	memcpy(buf, info->base + from, len);
>  	*retlen = len;
> +	zero_page_faulting();
>  
>  	return 0;
>  }
> @@ -908,7 +910,9 @@ static int cfi_mtd_write(struct mtd_info *mtd, loff_t to, size_t len,
>  	struct flash_info *info = container_of(mtd, struct flash_info, mtd);
>  	int ret;
>  
> +	zero_page_access();
>  	ret = write_buff(info, buf, (unsigned long)info->base + to, len);
> +	zero_page_faulting();
>  	*retlen = len;
>  
>          return ret;
> @@ -919,7 +923,9 @@ static int cfi_mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
>  	struct flash_info *info = container_of(mtd, struct flash_info, mtd);
>  	int ret;
>  
> +	zero_page_access();
>  	ret = cfi_erase(info, instr->len, instr->addr);
> +	zero_page_faulting();
>  	if (ret)
>  		return -EIO;
>  
> diff --git a/drivers/mtd/nor/cfi_flash.h b/drivers/mtd/nor/cfi_flash.h
> index cea6a8712c..99359a325e 100644
> --- a/drivers/mtd/nor/cfi_flash.h
> +++ b/drivers/mtd/nor/cfi_flash.h
> @@ -22,6 +22,8 @@
>  #include <io.h>
>  #include <linux/mtd/mtd.h>
>  
> +#include <zero_page.h>
> +
>  typedef unsigned long flash_sect_t;
>  
>  #if   defined(CONFIG_DRIVER_CFI_BANK_WIDTH_8)
> @@ -255,43 +257,59 @@ void flash_make_cmd(struct flash_info *info, u32 cmd, cfiword_t *cmdbuf);
>  
>  static inline void flash_write8(u8 value, void *addr)
>  {
> +	zero_page_access();
>  	__raw_writeb(value, addr);
> +	zero_page_faulting();
>  }
>  
>  static inline void flash_write16(u16 value, void *addr)
>  {
> +	zero_page_access();
>  	__raw_writew(value, addr);
> +	zero_page_faulting();
>  }
>  
>  static inline void flash_write32(u32 value, void *addr)
>  {
> +	zero_page_access();
>  	__raw_writel(value, addr);
> +	zero_page_faulting();
>  }
>  
>  static inline void flash_write64(u64 value, void *addr)
>  {
> +	zero_page_access();
>  	memcpy((void *)addr, &value, 8);
> +	zero_page_faulting();
>  }
>  
>  static inline u8 flash_read8(void *addr)
>  {
> +	zero_page_access();
>  	return __raw_readb(addr);
> +	zero_page_faulting();
>  }
>  
>  static inline u16 flash_read16(void *addr)
>  {
> +	zero_page_access();
>  	return __raw_readw(addr);
> +	zero_page_faulting();
>  }
>  
>  static inline u32 flash_read32(void *addr)
>  {
> +	zero_page_access();
>  	return __raw_readl(addr);
> +	zero_page_faulting();
>  }
>  
>  static inline u64 flash_read64(void *addr)
>  {
> +	zero_page_access();
>  	/* No architectures currently implement readq() */
>  	return *(volatile u64 *)addr;
> +	zero_page_faulting();
>  }
>  
>  /*


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