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[80.6.113.119]) by smtp.gmail.com with ESMTPSA id w18sm3803621wrn.55.2020.05.05.09.05.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2020 09:05:54 -0700 (PDT) From: Emil Velikov To: dri-devel@lists.freedesktop.org Subject: [PATCH 1/3] drm/dsi: use stack buffer in mipi_dsi_dcs_write() Date: Tue, 5 May 2020 17:03:27 +0100 Message-Id: <20200505160329.2976059-1-emil.l.velikov@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jani Nikula , Thierry Reding , emil.l.velikov@gmail.com Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Currently the function heap allocates when we have any payload. Where in many case the payload is 1 byte - ouch. From casual observation, vast majority of the payloads are smaller than 8 bytes - so use a stack array tx[8] to avoid the senseless kmalloc and kfree dance. Cc: Jani Nikula Cc: Thierry Reding Signed-off-by: Emil Velikov Reviewed-by: Thierry Reding --- drivers/gpu/drm/drm_mipi_dsi.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c index 55531895dde6..b96d5b4629d7 100644 --- a/drivers/gpu/drm/drm_mipi_dsi.c +++ b/drivers/gpu/drm/drm_mipi_dsi.c @@ -748,26 +748,26 @@ ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd, { ssize_t err; size_t size; + u8 stack_tx[8]; u8 *tx; - if (len > 0) { - size = 1 + len; - + size = 1 + len; + if (len > ARRAY_SIZE(stack_tx) - 1) { tx = kmalloc(size, GFP_KERNEL); if (!tx) return -ENOMEM; - - /* concatenate the DCS command byte and the payload */ - tx[0] = cmd; - memcpy(&tx[1], data, len); } else { - tx = &cmd; - size = 1; + tx = stack_tx; } + /* concatenate the DCS command byte and the payload */ + tx[0] = cmd; + if (data) + memcpy(&tx[1], data, len); + err = mipi_dsi_dcs_write_buffer(dsi, tx, size); - if (len > 0) + if (tx != stack_tx) kfree(tx); return err;