Hi, David > Subject: RE: [PATCH] pwm: pwm-imx27: Use 'dev' instead of dereferencing it > repeatedly > > From: Anson Huang > > Sent: 24 September 2019 10:00 > > Add helper variable dev = &pdev->dev to simply the code. > > > > Signed-off-by: Anson Huang <[email protected]> > > --- > > drivers/pwm/pwm-imx27.c | 13 +++++++------ > > 1 file changed, 7 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index > > 434a351..3afee29 100644 > > --- a/drivers/pwm/pwm-imx27.c > > +++ b/drivers/pwm/pwm-imx27.c > > @@ -290,27 +290,28 @@ MODULE_DEVICE_TABLE(of, > pwm_imx27_dt_ids); > > > > static int pwm_imx27_probe(struct platform_device *pdev) { > > + struct device *dev = &pdev->dev; > > struct pwm_imx27_chip *imx; > > > > - imx = devm_kzalloc(&pdev->dev, sizeof(*imx), GFP_KERNEL); > > + imx = devm_kzalloc(dev, sizeof(*imx), GFP_KERNEL); > > if (imx == NULL) > > return -ENOMEM; > > > > platform_set_drvdata(pdev, imx); > > > > - imx->clk_ipg = devm_clk_get(&pdev->dev, "ipg"); > > + imx->clk_ipg = devm_clk_get(dev, "ipg"); > > if (IS_ERR(imx->clk_ipg)) { > > - dev_err(&pdev->dev, "getting ipg clock failed with %ld\n", > > + dev_err(dev, "getting ipg clock failed with %ld\n", > > PTR_ERR(imx->clk_ipg)); > > return PTR_ERR(imx->clk_ipg); > > } > > > > - imx->clk_per = devm_clk_get(&pdev->dev, "per"); > > + imx->clk_per = devm_clk_get(dev, "per"); > > if (IS_ERR(imx->clk_per)) { > > int ret = PTR_ERR(imx->clk_per); > > > > if (ret != -EPROBE_DEFER) > > - dev_err(&pdev->dev, > > + dev_err(dev, > > "failed to get peripheral clock: %d\n", > > ret); > > Hopefully the compiler will optimise this back otherwise you've added > another local variable which may cause spilling to stack. > For a setup function it probably doesn't matter, but in general it might have > a > small negative performance impact. > > In any case this doesn't shorten any lines enough to remove line-wrap and > using &pdev->dev is really one less variable to mentally track when reading > the code.
Do we know which compiler will optimize this? I saw many of the patches doing this to avoid a lot of dereference, I understand it does NOT save lines, but my intention is to avoid dereference which might save some instructions. I thought saving instructions is more important. So now there are different opinion about doing this? Anson
