linux-kernel - Re: [PATCH] staging: rts5208: Convert kmap() to kmap_local

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Date:   Mon, 28 Mar 2022 08:41:53 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Philip <benjamin.philip495@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Charlie Sands <sandsch@...thvilleschools.net>,
        Mitali Borkar <mitaliborkar810@...il.com>,
        Colin Ian King <colin.king@...el.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: rts5208: Convert kmap() to kmap_local_page()

On Mon, Mar 28, 2022 at 01:24:40PM +0200, Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated and kmap_local_page() is faster.
> Use kmap_local_page() in place of kmap().

Thanks for the patch!  I have just a couple of comments.

kmap_local_page() is not necessarily faster than kmap() but it is more correct
in this case.  You should mention why.

Also to help with kmap_local_page() there are a number of helpers implemented
in highmem.h for things like memcpy, memmove, etc.

Check out memcpy_page() for this use case.

Thank you!
Ira

> 
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>  drivers/staging/rts5208/rtsx_transport.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/rts5208/rtsx_transport.c b/drivers/staging/rts5208/rtsx_transport.c
> index 805dc18fac0a..de690d7ee5e3 100644
> --- a/drivers/staging/rts5208/rtsx_transport.c
> +++ b/drivers/staging/rts5208/rtsx_transport.c
> @@ -92,13 +92,13 @@ unsigned int rtsx_stor_access_xfer_buf(unsigned char *buffer,
>  			while (sglen > 0) {
>  				unsigned int plen = min(sglen, (unsigned int)
>  						PAGE_SIZE - poff);
> -				unsigned char *ptr = kmap(page);
> +				unsigned char *ptr = kmap_local_page(page);
>  
>  				if (dir == TO_XFER_BUF)
>  					memcpy(ptr + poff, buffer + cnt, plen);
>  				else
>  					memcpy(buffer + cnt, ptr + poff, plen);
> -				kunmap(page);
> +				kunmap_local(ptr);
>  
>  				/* Start at the beginning of the next page */
>  				poff = 0;
> -- 
> 2.34.1
>